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Title: Chemistry
Description: This note is for 100 level students this note will guide you in everything about chemistry
Description: This note is for 100 level students this note will guide you in everything about chemistry
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CHEMISTRY
HIGHER SECONDARY - FIRST YEAR
VOLUME - I
REVISED BASED ON THE RECOMMENDATIONS OF THE
TEXT BOOK DEVELOPMENT COMMITTEE
A Publication Under
Government of Tamilnadu
Distribution of Free Textbook Programme
(NOT FOR SALE)
Untouchability is a sin
Untouchability is a crime
Untouchability is inhuman
TAMILNADU
TEXTBOOK CORPORATION
College Road, Chennai - 600 006
© Government of Tamilnadu
First Edition - 2004
Revised Edition - 2007
CHAIRPERSON & AUTHOR
Dr
...
BALASUBRAMANIAN
Professor of Chemistry (Retd
...
REVIEWERS
AUTHORS
Dr
...
KRISHNAMURTHI
Professor of Chemistry
Presidency College (Autonomous)
Chennai - 600 005
...
S
...
MEENAKSHISUNDRAM
Professor of Chemistry,
Annamalai University,
Annamalai Nagar 608 002
...
M
...
Dr
...
RAMESH
Senior Lecturer in Chemistry,
Bharathidasan University
Trichirapalli 620 024
...
M
...
DR
...
SANTHANALAKSHMI
Professor of Physical Chemistry
University of Madras
Chennai - 600 025
...
V
...
N
...
Price : Rs
...
T
...
G
...
Higher Secondary School
Chennai - 600 101
...
S
...
G
...
Hr
...
School
Kilpauk, Chennai - 600 010
...
K
...
G
...
Sec
...
Dr
...
RAJALAKSHMI
P
...
Teacher in Chemistry,
Chettinad Vidyashram
Chennai - 600 028
...
This book has been printed on 60 G
...
M paper
Printed by Offset at :
(ii)
PREFACE
Where has chemistry come from ? Throughout the history of the human
race, people have struggled to make sense of the world around them
...
The ancient Greek philosophers had their own ideas of the
nature of matter, proposing atoms as the smallest indivisible particles
...
Alchemy was a mixture of scientific investigation and mystical quest, with
strands of philosophy from Greece, China, Egypt and Arabia mixed in
...
Improbable
as these ideas might seem today, the alchemists continued their quests for around
2000 years and achieved some remarkable successes, even if the elixir of life
and the philosopher’s stone never appeared
...
During the nineteenth
century chemists worked steadily towards an understanding of the relationships
between the different chemical elements and the way they react together
...
This brought
order to the chemical world, and from then on chemists have never looked back
...
It also looks for an
academic understanding of how matter works and how the environment might
be protected from the source of pollutants
...
The present book is written after following the revised syllabus, keeping in view
with the expectations of National Council of Educational Research & Training
(NCERT)
...
A lot of self evaluation questions, like, choose the best
answer, fill up the blanks and very short answer type questions are given in all
chapters
...
They must be prepared to answer the questions and problems from the
entire text
...
Sufficient reference books are suggested so as to enable the students to
acquire more informations about the concepts of chemistry
...
V
...
- Mass/Mass relationship Methods of expressing concentration of solution - Calculations on principle of
volumetric analysis - Determination of equivalent mass of an element Determination of equivalent mass by oxide, chloride and hydrogen displacement
method - Calculation of equivalent mass of an element and compounds Determination of molar mass of a volatile solute using Avogadro’s hypothesis
...
Unit 3 - General Introduction to Metallurgy
Ores and minerals - Sources from earth, living system and in sea Purification of ores-Oxide ores sulphide ores magnetic and non magnetic ores Metallurgical process - Roasting-oxidation - Smelting-reduction - Bessemerisation
- Purification of metals-electrolytic and vapour phase refining - Mineral wealth of
India
...
- Quantum designation of electron - Pauli’s exclusion principle
- Hund’s rule of maximum multiplicity - Aufbau principle - Stability of orbitals Classification of elements based on electronic configuration
...
Unit 6 - Group-1s Block elements
Isotopes of hydrogen - Nature and application - Ortho and para hydrogen
- Heavy water - Hydrogen peroxide - Liquid hydrogen as a fuel - Alkali metals
- General characteristics - Chemical properties - Basic nature of oxides and
hydroxides - Extraction of lithium and sodium - Properties and uses
...
Unit 8 -p- Block elements
General characteristics of p-block elements - Group-13
...
properties - Uses of Boron
and its compounds - Carbon group - Group -14 - Allotropes of carbon Structural difference of graphite and diamond - General physical and chemical
properties of oxides, carbides, halides and sulphides of carbon group - Nitrogen
- Group-15 - Fixation of nitrogen - natural and industrial - HNO3-Ostwald process
- Uses of nitrogen and its compounds - Oxygen - Group-16 - Importance of
molecular oxygen-cell fuel - Difference between nascent oxygen and molecular
oxygen - Oxides classification, acidic basic, amphoteric, neutral and peroxide Ozone preparation, property and structure - Factors affecting ozone layer
...
Unit 10 - Gaseous State
Four important measurable properties of gases - Gas laws and ideal gas
equation - Calculation of gas constant ‘‘R” - Dalton’s law of partial pressure Graham’s law of diffusion - Causes for deviation of real gases from ideal behaviour
- Vanderwaal’s equation of state - Critical phenomena - Joule-Thomson effect
and inversion temperature - Liquefaction of gases - Methods of Liquefaction of
gases
...
Unit 12 - Colligative Properties
Concept of colligative properties and its scope - Lowering of vapour
pressure - Raoul’s law - Ostwald - Walker method - Depression of freezing
point of dilute solution - Beckmann method - Elevation of boiling point of dilute
solution - Cotrell’s method - Osmotic pressure - Laws of Osmotic pressure Berkley-Hartley’s method - Abnormal colligative properties Van’t Hoff factor
and degree of dissociation
...
Unit 14 - Chemical Equilibrium - I
Scope of chemical equilibrium - Reversible and irreversible reactions Nature of chemical equilibrium - Equilibrium in physical process - Equilibrium in
chemical process - Law of chemical equilibrium and equilibrium constant Homogeneous equilibria - Heterogeneous equilibria
...
ORGANIC CHEMISTRY
Unit 16 - Basic Concepts of Organic Chemistry
Catenation - Classification of organic compounds - Functional groups Nomenclature - Isomerism - Types of organic reactions - Fission of bonds Electrophiles and nucleophiles - Carbonium ion Carbanion - Free radicals Electron displacement in covalent bond
...
Unit 18 - Detection and Estimation of Elements
Detection of carbon and hydrogen - Detection of Nitrogen - Detection of
halogens - Detection of sulphur - Estimation of carbon and hydrogen - Estimation
of Nitrogen - Estimation of sulphur - Estimation of halogens
...
Unit 20 - Aromatic Hydrocarbons
Aromatic Hydrocarbons - IUPAC nomenclature of aromatic hydrocarbons
- Structure of Benzene - Orientation of substituents on the benzene ring Commercial preparation of benzene - General methods of preparation of Benzene
and its homologues - Physical properties - Chemical properties - Uses Carcinogenic and toxic nature
...
(ix)
CHEMISTRY PRACTICALS FOR STD XI
I
...
II
...
1
...
Preparation of Mohr’s Salt
3
...
Preparation of Iodoform
5
...
Identification of one cation and one anion from the following
...
Anions : Borate, Sulphide, Sulphate, Carbonate, Nitrate, Chloride, Bromide
...
Determination of Melting point of a low melting solid
...
Acidimetry Vs Alkalimetry
1
...
2
...
Titration of HCl Vs Na2CO3
4
...
PAGE NO
...
Chemical Calculations
1
2
...
Atomic Structure - I
57
4
...
Group 1 s-Block elements
110
6
...
p-Block elements
146
Physical Chemistry
8
...
Gaseous state - I
194
(xi)
INORGANIC CHEMISTRY
1
...
Recognise the value of Avogadro number and its significance
...
Know about the empirical and molecular formula and understand the
method of arriving molecular formula from empirical formula
...
Know about balancing the equation in its molecular form
...
Know about the method of balancing redox equation using oxidation
number
...
1 Formula Weight (FW) or Formula Mass
The formula weight of a substance is the sum of the atomic weights of
all atoms in a formula unit of the compound, whether molecular or not
...
44 amu (22
...
45 amu from Cl)
...
On the other hand,
the molecular weight and the formula weight calculated from the molecular
formula of a substance are identical
...
Solution
a
...
0 amu
1 x AW of H
= 1
...
45 = 106
...
4 amu
1
The answer rounded to three significant figures is 119 amu
...
Iron(III)Sulfate
2 x Atomic weight of Fe = 2 x 55
...
6 amu
3 x Atomic weight of S
= 3 x 32
...
3 amu
3 x 4 Atomic weight of O =12x16= 192
...
9 amu
The answer rounded to three significant figures is 4
...
Problems for Practice
Calculate the formula weights of the following compounds
a
...
glucose (C6H12O6)
e
...
NaOH
f
...
Mg(OH)2
g
...
2 Avogadro's Number (NA)
The number of atoms in a 12-g sample of carbon - 12 is called
Avogadro's number (to which we give the symbol NA)
...
0221367 x 1023,
which is 6
...
A mole of a substance contains Avogadro's number of molecules
...
023 x 1023 ethanol molecules
...
64 g of SO2 contains
6
...
2
...
T
...
contains
6
...
Similarly the molecular mass of CO2 is 44 g mol-1
...
023 x 1023 molecules of CO2
...
24 x 10-2m3 of CO2 at S
...
P contains
6
...
1
...
Some times, we have to take the atoms or
molecules of different reactants in a definite ratio
...
Consider the following reaction
2 H2 + O2 → 2H2O
In this reaction one molecule of oxygen reacts with two molecules of
hydrogen
...
But atoms and molecules are so small in size that is not possible to
count them individually
...
According to this concept number of particles of the substance
is related to the mass of the substance
...
(i
...
One mole
One mole of oxygen molecule
One mole of oxygen atom
One mole of ethanol
6
...
023 x 1023 oxygen molecules
6
...
023 x 1023 ethanol molecules
=
=
=
=
In using the term mole for ionic substances, we mean the number of
formula units of the substance
...
023 x 1023 Na2CO3 units
...
023 x 1023 Na+ ions and one CO32ions and 1 x 6
...
When using the term mole, it is important to specify the formula of the
unit to avoid any misunderstanding
...
A mole of oxygen atom (with the formula O) contains 6
...
A mole of oxygen molecule (formula O2) contains
6
...
e) 2 x 6
...
Molar mass
The molar mass of a substance is the mass of one mole of the
substance
...
3
Mass
Molar mass = ____
mole
Eg
...
Problems
Solved Problems
1
...
What is the mass in grams of a hydrogen chloride, HCl?
Solution
1
...
5 amu, so the molar mass of Cl is
35
...
Dividing 35
...
023 x 1023 gives the mass of
one atom
...
5 g
Mass of a Cl atom = __________
6
...
90 x 10-23 g
2
...
01 + 35
...
5 amu
...
5 g HCl
36
...
02 x1023
= 6
...
What is the mass in grams of a calcium atom, Ca?
2
...
Calcualte the mass (in grams) of each of the following species
...
Na atom b
...
CH3Cl molecule d
...
3
...
4
i
...
How many moles of a given formula unit does a given mass of
substance contain
...
To illustrate, consider the conversion of grams of ethanol, C2H5OH, to
moles of ethanol
...
1 g/mol, So, we write
1 mol C2H5OH = 46
...
1g C2H5OH
...
1 g C2H5OH/1 mol
C2H5OH)
...
0g of
ethanol, C2H5OH
...
0g
C2H5OH to moles C2H5OH by multiplying by the appropriate conversion
factor
...
0g C H OH x _____________
2
5
46
...
217 mol C2H5 OH
1
...
2 Converting Moles of Substances to Grams
Solved Problems
1
...
A
chemist determines from the amounts of elements that 0
...
Solution
The molar mass of ZnI2 is 319 g/mol
...
0654 mol ZnI x __________
2
1 mol ZnI2
= 20
...
H2O2 is a colourless liquid
...
Dilute aqueous solutions are
used as a bleach
...
909 mol
H2O2 in 1
...
What is the mass of H2O2 in this volume of
solution?
...
Boric acid, H3BO3 is a mild antiseptic and is often used as an eye
wash
...
543 mol H3BO3
...
3
...
A sample contains 0
...
Calculate the mass of CS2 in the sample
...
6 g of
lead(II)chromate is obtained as a precipitate
...
e) 1 mol PbCrO4 = 323 g
PbCrO4
Therefore,
45
...
PbCrO4
___________________________
323 g PbCrO4
= 0
...
Nitric acid, HNO3 is a colourless, corrosive liquid used in the
manufacture of Nitrogen fertilizers and explosives
...
5 g sample of HNO3
was poured into a beaker
...
a
...
e
...
Obtain the moles of substances in the following
...
43 g of C
b
...
05 g Br2
d
...
4 g Li2 CO3
76g C4 H10
2
...
7
...
153 g Al2 (SO4)3
41
...
46 g sample of hydrogen chloride,
HCl?
Note: The number of molecules in a sample is related to moles of
compound (1 mol HCl = 6
...
Therefore if you
first convert grams HCl to moles, then you can convert moles to number of
molecules)
...
46g HClx
1 mol HCl
x
6
...
5g HCl
23
HClmolecul
es
1 mol HCl
= 5
...
How many molecules are there in 56mg HCN?
2
...
b
...
Calculate the following
Number of molecules in 43g NH3
Number of atoms in 32
...
46 g Li
1
...
For most ionic substances, the empirical formula is the formula of the
compound
...
For
example, the formula of sodium peroxide, an ionic compound of Na+ and
O22-, is Na2O2
...
Thus empirical formula tells
you the ratio of numbers of atoms in the compound
...
i
...
This will
give the relative number of moles of various elements present in the
compound
...
Divide the quotients obtained in the above step by the smallest of them
so as to get a simple ratio of moles of various elements
...
Multiply the figures, so obtained by a suitable integer of necessary in
order to obtain whole number ratio
...
Finally write down the symbols of the various elements side by side and
put the above numbers as the subscripts to the lower right hand of each
symbol
...
Solved Problem
A compound has the following composition Mg = 9
...
01%, 0
= 26
...
22, what is its empirical formula?
[Mg = 24, S = 32, O = 16, H = 1]
Solution
Element
Magnesium
Sulphur
Oxygen
Water
Relative No
...
76
0
...
76 ____ = 0
...
406
0
...
01
_____ = 1
13
...
406
%
32
26
...
01 _____ = 1
...
406
1
...
22
51
...
846
18
2
...
ratio
1
1
4
0
...
406
Hence the empirical formula is Mg SO4
...
Problems for Practice
8
7
1
...
4%, C = 11
...
3% calculate its empirical
formula [Na = 23, C = 12, O = 16]
...
What is the simplest formula of the compound which has the
following percentage composition: Carbon 80%, hydrogen 20%
...
A compound on analysis gave the following percentage
composition: C - 54
...
09%, 0 = 36
...
4
...
Example
The molecular formula of acetylene, C2H2 is equivalent to (CH)2, and
the molecular formula of benzene, C6H6 is equivalent to (CH)6
...
For any molecular compound
...
Where `n' is the whole number of empirical formula units in the molecule
...
Calculate the empirical formula
ii
...
iii
...
iv
...
Solved Problem
1
...
54%, H, 9
...
36
...
Find out the molecular formula of the
compound
...
of
moles
Simple ratio
moles
H
O
54
...
09
12
9
...
09
4
...
27
9
...
36
1
36
...
27
2
...
27
____ = 1
16
C
54
...
53
Simplest whole
No
...
27
Empirical formula is C2 H4 O
...
A compound on analysis gave the following percentage
composition: Na=14
...
97%, H = 6
...
5%, calcualte the
molecular formula of the compound on the assumption that all the
hydrogen in the compound is present in combination with oxygen as water
of crystallisation
...
Solution :- Calculation of empirical formula
Element
%
Relative No
...
ratio
S
H
O
2
0
...
31
___ = 1
1
0
...
22
___ = 20
20
1
69
...
34
0
...
34
___ = 14
14
16
Na
0
...
31
14
...
31 ____ = 0
...
97
9
...
31
32
6
...
22 ___ = 6
...
5
The empirical formula is Na2 SH20O14
Calculation of Molecular formula
Empirical formula mass
= (23 x 2) + 32 + (20 x 1) + (16 x 14)
= 322
n
Molecular mass
___________________
=
Empirical formula mass
322
____ = 1
=
322
Hence molecular formula = Na2 SH20 O14
11
Since all hydrogens are present as H2O in the compound, it means 20
hydrogen atoms must have combined
...
The remaining (14 - 10 = 4) atoms of oxygen should be
present with the rest of the compound
...
10H2O
...
An organic compound was found to have contained carbon =
40
...
55% and Nitrogen = 23
...
Its vapour - density was
found to be 29
...
What is the molecular formula of the compound?
Ans:- C2H5NO
2
...
Its vapour density is 75
...
Ans:- C2H3O3, C4H6O6
3
...
6% carbon, 3
...
Calcualte the molecualr formula of the
acid
...
What is the simplest formula of the compound which has the
following percentage composition: carbon 80%, Hydrogen 20%, If the
molecular mass is 30, calcualte its molecular formula
...
5 Stoichiometry Equations
Stoichiometry
Stoichiometry is the calculation of the quantities of reactants and
products involved in the chemical reaction
...
A stoichiometric equation is a short scientific representation of a
chemical reaction
...
In order to write the stoichiometric equation correctly, we must
know the reacting substances, all the products formed and their chemical
formula
...
The formulae of the reactant must be written on the left side of
12
arrow with a positive sign between them
...
The formulae of the products formed are written on the right side of
the arrow mark
...
The equation thus obtained is called skeleton equation
...
But in many cases the
skeleton equation is not a balanced one
...
The skeletal equation for this reaction is
Pb(NO3)2 → PbO + NO2 + O2
iv
...
v
...
vi
...
,
may be noted above (or) below the arrow of the equation
...
An upward arrow (↑) is placed on the right side of the formula of a
gaseous product and a downward arrow (↓) on the right side of the
formulae of a precipitated product
...
All the reactants and products should be written as molecules
including the elements like hydrogen, oxygen, nitrogen, fluorine chlorine,
bromine and iodine as H2, O2, N2, F2, Cl2, Br2 and I2
...
5
...
The
several steps involved in balancing chemical equation are discussed below
...
The number of atoms of hydrogen on the
left side is two but on the right side it is one
...
Then the equation becomes
H2 + Br2 →
2HBr
This is the balanced (or) stoichiometric equation
...
The skeletal equation is
KMnO4 + HCl → KCl + MnCl2 + H2O + Cl2
If an element is present only one substance in the left hand side of the
equation and if the same element is present only one of the substances in
the right side, it may be taken up first while balancing the equation
...
There are
L
...
S
...
H
...
KMnO4 + 8HCl → KCl + MnCl2 + 4H2O + Cl2
Of the eight chlorine atoms on the left, one is disposed of in KCl and
two in MnCl2 leaving five free chlorine atoms
...
5
...
All such processes fall in the category of
specific type of chemical reactions called reduction - oxidation (or) redox
reactions
...
, are also based upon the redox reactions
...
According to the
classical concept, oxidation and reduction may be defined as,
Oxidation is a process of addition of oxygen (or) removal of hydrogen
Reduction is a process of removal of oxygen (or) addition of hydrogen
...
Thus, H2S is oxidised
and Cl2 is reduced
...
The loss
of electrons results in the increase of positive charge (or) decrease of
negative of the species
...
Fe2+→ Fe3+ + e- [Increase of positive charge]
Cu→ Cu2+ + 2e- [Increse of positive charge]
15
The species which undergo the loss of electrons during the reactions are
called reducing agents or reductants
...
Reduction
Reduction is a process in which an atom (or) a group of atoms taking
part in chemical reaction gains one (or) more electrons
...
For example,
Fe3+ + e- →Fe2+ [Decrease of positive charges]
Zn2+ + 2e- → Zn [Decrease of positive charges]
The species which undergo gain of electrons during the reactions are
called oxidising agents (or) oxidants
...
Oxidation Number (or) Oxidation State
Oxidation number of the element is defined as the residual charge
which its atom has (or) appears to have when all other atoms from the
molecule are removed as ions
...
General Rules for assigning Oxidation Number to an atom
The following rules are employed for determining oxidation number of
the atoms
...
The oxidation number of the element in the free (or) elementary
state is always Zero
...
The oxidation number of the element in monoatomic ion is equal to
the charge on the ion
...
The oxidaton number of fluorine is always - 1 in all its compounds
...
Hydrogen is assigned oxidation number +1 in all its compounds
except in metal hydrides
...
, the oxidation number of hydrogen is -1
...
Oxygen is assigned oxidation number -2 in most of its compounds,
however in peroxides like H2O2, BaO2, Na2O2, etc its oxidation number is 1
...
6
...
In case of polyatomic ion the sum of oxidation numbers of all its atoms is
equal to the charge on the ion
...
In binary compounds of metal and non-metal the metal atom has
positive oxidation number while the non-metal atom has negative oxidation
number
...
Oxidation number of K in KI is +1 but oxidation number
of I is - I
...
In binary compounds of non-metals, the more electronegative atom
has negative oxidation number, but less electronegative atom has positive
oxidation number
...
Problem
Calculate the oxidation number of underlined elements in the following
species
...
C in CO2
...
Oxidation number of each
O atom = -2
...
As it is neutral molecule, the sum must be equal to zero
...
Cr in Cr2O72-
...
Oxidation number of
each oxygen atom =-2
...
Thus, 2x - 14 = -2
17
2x = +12
x
= 12/2
x
= 6
Problems for Practice
Calculate the oxidation number of underlined elements in the following
species
...
MnSO4
b
...
HNO3
e
...
K2MnO4
Oxidation and Reduction in Terms of Oxidation Number
Oxidation
"A chemical process in which oxidation number of the element
increases"
...
Eg
...
Decrease of Oxidation
Number (Br)
+1 -2
H2S
+
0
Br2
→
+1 -1
2HBr
+
0
S
Increase of oxidation
Number (S)
In the above reaction, the oxidation number of bromine decreases from
0 to -1, thus it is reduced
...
Hence H2S is oxidised
...
i
...
18
ii
...
In the above reaction H2S is reducing agent while Br2 is oxidising
agent
...
MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O
Solution
Increase of Oxidation Number
+4
MnO2
+
-1
4HCl →
+2
MnCl2
+
0
Cl2
+1 -2
+ 2H2 O
Decrease of oxidation Number
As it is clear, manganese decrease its oxidation number from +4 to +2
...
Chlorine atom in
HCl increases its oxidation number from -1 to 0
...
Balancing Redox reaction by Oxidation Number Method
The various steps involved in the balancing of redox equations
according to this method are :
1
...
2
...
Multiply the increase (or) decrease of oxidation number of atoms
undergoing the change
...
Equalise the increase in oxidation number and decrease in oxidation
number on the reactant side by multiplying the respective formulae with
19
suitable integers
...
Balance the equation with respect to all atoms other than O and H
atoms
...
Balance oxygen by adding equal number of water molecules to the
side falling short of oxygen atoms
...
H atoms are balanced depending upon the medium in same way as
followed in ion electron method
...
MnO2 + Cl-
2+
→ Mn + Cl2 + H2O
in acidic medium
Step 1
MnO2 + Cl- → Mn2+ + Cl2 + H2O
Step 2
O
...
Decreases by 2 per Mn
4+
+
MnO2
-1
Cl
+2
Mn
+
Cl2
+ H2O
O
...
increases by 1 per Cl
Step 3
Equalise the increase / decrease in O
...
MnO2 + 2 Cl- →Mn2+ + Cl2 + H2O
Step 4
Balance other atoms except H and O
...
Step 5
Balance O atoms by adding H2O molecules to the side falling short of
oxygen atoms
...
Mg + NO3- → Mg2+ + N2O + H2O
(in acidic medium)
3+
2
...
S2- + NO3- → NO + S
4
...
Cl2 + OH- → Cl- + ClO3- + H2O
1
...
From a stoichiometric chemical
equation, we know how many molecules of reactant react and how many
molecules of products are formed
...
The parts
by mass are usually in kg
...
1
...
1 Mass / Mass Relationship
Example 1
Calculate the mass of CO2 that would be obtained by completely
dissolving 10kg of pure CaCO3 in HCl
...
4 kg of CO2
Example 2
Calculate the mass of oxygen obtained by complete decomposition of
10kg of pure potassium chlorate (Atomic mass K=39, O=16 and Cl = 35
...
5+48=122
...
According to the Stoichiometric equation written above (2 x 122
...
-3
10kg of KClO3 gives =
3 x 32 x 10-3
____________ x 10
2 x 122
...
92 kg of O2
Example 3
Calculate the mass of lime that can be prepared by heating 200 kg of
limestone that is 90% pure CaCO3
CaCO3
→ CaO + CO2
100 kg x 10-3 56 kg x 10-3
90
200 kg of 90% pure CaCO
= 200 x ___
3
100
= 180 kg pure CaCO3
100x10-3 kg of pure CaCO3 on heating gives 56 x 10-3 kg of Ca0
56 x 10-3 x 180
____________
180 kg of CaCO =
3
100 x 10-3
gives on heating
=
100
...
7 Methods of Expressing the concentration of solution
22
The concentration of a solution refers to the amount of solute present in
the given quantity of solution or solvent
...
1
...
It is expressed in g L-1
...
X x 1000
= _______
V
Molarity (M)
Molarity of a solution is defined as the number of gram-moles of solute
dissolved in 1 litre of a solution
Molarity
No
...
mass
1000
_____
V
Molarity is represented by the symbol M
...
1M solution of Sugar, C12H22O11 (mol
...
2 g of sugar is present in one litre (1000 cm3) of the solution
...
Normality
Normality of a solution is defined as the number of gram equivalents of
the solute dissolved per litre of the given solution
...
mass
1000 mL
_______
V
Normality is represented by the symbol N
...
mass of the solute
Example
A 0
...
mass = 49), means that
4
...
4
...
Mathematically,
Molality
Number of moles of solute
= _______________________
Mass of solvent in kilograms
"If X grams of the solute is dissolved in b grams of the solvent", then
24
Molality
X
1000g
________ x _____
=
Mol
...
Example
A 0
...
mass = 180), means that 18g
of glucose is present in 1000g (or one kilogram) of water
...
Mole Fraction
Mole fraction is the ratio of number of moles of one component (Solute
or Solvent) to the total number of moles of all the components (Solute and
Solvent) present in the Solution
...
Let us suppose that a
solution contains 2 components A&B and suppose that nA moles of A and
nB moles of B are present in the solution
...
(1)
nB
________
...
Therefore, if mole fraction
of one component in a binary solution is known, that of the other can be
calculated
...
4
...
Calculate the molarity of
solution
...
5g
Mass
4
...
075mol
Volume of Solution
100
____ L
= 1000 ml =
1000
= 0
...
075
= _____ mol = 0
...
12
2
...
15g of hydrated
oxalic acid (H2C2O4
...
mass = 126)
...
15g
Mol
...
Mass
26
3
...
05 equiv
63 g equiv-1
250
Volume of solution = 250ml = L = 0
...
05 equiv
=
= 0
...
25 L
3
...
0g of
urea (mol
...
Solution
Mass of solute
=
3
...
0 g
________ = 0
...
25 kg
1000
Moles of Solute
__________________
=
Mass of Solvent in kg
...
05 Mol
________ = 0
...
25 kg
27
Problems for practice
1
...
3m NH3, solution needed to prepare 1L
of 0
...
Ans:-6
...
How would you make up 425 mL of 0
...
0%
HNO3? The density of 68
...
41g/mL
...
25 mL
3
...
3 M H2SO4 and 200 mL of 1
...
1M
4
...
850g of
ammonia (NH3) in 100g of water
...
5m
1
...
8
...
Suppose
substance A in solution reacts with substance B
...
Titration is a procedure for determining the amount of substance A by
adding a carefully measured volume of a solution of A with known
concentration of B untill the reaction of A and B is just completed
...
Law
"Equal volume of equinormal solutions exactly neutralise the other
solution having same concentration and volume"
...
N1, N2 -
Strength of solutions
...
What volume of 6M HCl and 2M HCl should be mixed to get one
litre of 3M HCl?
Solution
Suppose the volume of 6M HCl required to obtain 1L of 3M HCl = XL
Volume of 2M HCl required = (1-x)L
Applying the molarity equation
+ M2V2
= M3V3
M1V1
6MHCl+ 2MHCl= 3MHCl
6x+2(1-x)
= 3x1
6x+2-2x
= 3
4x
= 1
x
= 0
...
25L
Volume of 2M HCl required
= 0
...
How much volume of 10M HCl should be diluted with water to
prepare 2
...
Solution
N1V1
= N2V2
10N HCl = 5N HCl
10xV1
= 5 x 2
...
00
= _______
10
= 1
...
NiSO4 reacts with Na3PO4 to give a yellow green precipitate of
Ni3(PO4)2 and a solution of Na2SO4
...
375M NiSO4 will react with 45
...
265M
Na3PO4?
2
...
250M HNO3 reacts with 42
...
150M
Na2CO3 in the following reaction?
2HNO3(aq) + Na2CO3(aq) → 2NaNO3(aq) + H2O(aq)+CO2(g)
3
...
1 mL of 0
...
How many
mL of 0
...
Na2CO3(aq) + Ca(OH)2(aq) → CaCO3(aq) + 2NaOH(aq)
1
...
2
Determination of equivalent masses of elements
Equivalent masses can be determined by the following methods:
1
...
3
...
Hydrogen displacement method
Oxide method
Chloride method
Metal displacement method
Hydrogen displacement method
This method is used to determine the equivalent mass of those metals
such as magnesium, zinc and aluminium which react with dilute acids and
readily displace hydrogen
...
Problem 1
0
...
0198 g of
hydrogen at S
...
P
...
0
...
0198 g of hydrogen
30
The mass of the metal which will displace
1
...
008 x 0
...
0198
The equivalent mass of the metal = 27
...
magnesium, copper etc
...
Magnesium forms its oxide directly on heating
2Mg + O2 → 2 MgO
In the case of copper, its oxide is obtained in an indirect manner i
...
copper is dissolved in concentrated nitric acid and the copper(II) nitrate
formed after evaporation is strongly heated to give copper (II) oxide
...
w1
______ x 8
∴8 g of oxygen will combine with
w2 - w1
This value represents the equivalent mass of the metal
...
635 g of a metal gives on oxidation 0
...
Calculate
the equivalent mass of the metal
...
795g
Mass of the metal
= 0
...
795 - 0
...
16g
0
...
635 g of a metal
∴ 8 g of oxygen will combine with
8 x 0
...
75 of the metal
0
...
75g equiv-1
Chloride Method
The equivalent mass of those elements which readily form their
chlorides can be determined by chloride method
...
The
resulting silver nitrate solution is treated with pure hydrochloric acid when
silver chloride is precipitated
...
Thus
from the masses of the metal and its chloride, the equivalent mass of the
metal can be determined as follows :
Calculations
Mass of the metal
= w1 g
Mass of the metal chloride = w2 g
Mass of chlorine
= (w2 - w2) g
(w2 - w1) g of chlorine has combined with w1 of the metal
35
...
46 x w1
_________ g of the metal
(w2 - w1)
This value gives the equivalent mass of the metal
...
If any
three quantities are known, the fourth one can readily be calculated using
the above expression
...
8
...
The number of
replaceble hydrogen atoms present in a molecule of the acid is referred to
its basicity
...
008 part by mass of replaceble hydrogen atom
...
of replaceble hydrogen atom
(or)
=
molar mass of the acid
___________________
basicity of the acid
For example, the basicity of sulphuric acid is 2
...
Equivalent mass of the base
Equivalent mass of a base is the number of parts by mass of the base
which contains one replaceable hydroxyl ion or which completely
neutralises one gram equivalent of an acid
...
Sodium
hydroxide, potassium hydroxide, ammonium hydroxide are examples of
monoacidic bases
...
Equivalent mass of a salt
Equivalent mass of a salt is a number of parts by mass of the salt that is
produced by the neutralisation of one equivalent of an acid by a base
...
KOH + HCl → KCl + H2O
Therefore, the equivalent mass of the salt is equal to its molar mass
...
Equivalent mass of an oxidising agent
The equivalent mass of an oxidising agent is the number of parts by
mass which can furnish 8 parts by mass of oxygen for oxidation either
directly or indirectly
...
In acid
medium potassium permanganate reacts as follows
2 KMnO4 + 3 H2SO4 → K2SO4 + 2 MnSO4 + 3 H2O + 5 [O]
316
80
80 parts by mass of oxygen are made available from 316 parts by mass
of KMnO4
8 parts by mass of oxygen will be furnished by
316 x 8
______ = 3
...
6g equiv-1
5
...
34
(i) Ferrous sulphate reacts with an oxidising agent in acid medium
according to the equation
2 FeSO4 + H2SO4 + (O) → Fe2 (SO4)3 + H2O
2 x 152g
16g
16 parts by mass of oxygen oxidised 304 parts by mass of ferrous
sulphate
8 parts by mass of oxygen will oxidise 304/16 x 8 parts by mass of
ferrous sulphate
...
The equivalent mass of crystalline ferrous sulphate, FeSO4 7H2O is
152 + 126 = 278
126 is the mass corresponding to 7 moles of water
...
8 parts by mass of oxygen will oxidise 90/16 x 8 = 45 parts by mass of
anhydrous oxalic acid
...
2H2O=126/2
= 63 g equiv-1
...
8
...
The vapour displaces its
own volume of air
...
The volume of the vapour at
s
...
p is then calculated
...
24 x 10-2m3 of the vapour at
S
...
P
...
This value represents the molecular mass of the
substance
...
Sample tube
2
...
Victor-Meyer tube
4
...
1 Determination of molecular mass by victor-Meyers method
The apparatus consists of an inner Victor-Meyer tube, the lower end of
which is in the form of a bulb
...
The Victor-Meyer tube is surrounded by
an outer jacket
...
A small quantity of glass wool or asbestos fiber
covers the bottom of the Victor-Meyer tube to prevent breakage when the
bottle containing the substance is dropped in
...
A small quantity of the
substance is exactly weighed in a small stoppered bottle and quickly
dropped in the heated Victor-Meyer tube and corked immediately
...
The volume of air in the graduated tube is
measured by taking it out by closing its mouth with the thumb and dipping
36
it in a jar full of water
...
The atmospheric
pressure and laboratory temperature are noted
...
T1 K
Let the aqueous tension be p Nm-2 at that temperature
...
013 x 105 Nm-2
Let the volume of the vapour at standard temperature and pressure be
V0 m3
From the gas equation, it follows
P0V0
____
T0
V0
P1 V1
= _____
T1
P1V1
= _____ x
T1
T0
____
P0
3
The mass of V0 m of vapour at s
...
p is w g
...
24 x 10-2 m3 of the vapour at s
...
p
...
24x10-2xW
__________
V0
The value thus calculatd gives the molecular mass
37
Molecular mass
= 2 x vapour density
Molecular mass
_____________
Vapour density=
2
Problem
In the determination of molecular mass by Victor-Meyer's Method
0
...
696 x 10-4m3 of moist air at 303 K
and at 1 x 105 Nm-2 pressure
...
242 x 103
Nm-2
...
Mass of the organic compound
= 0
...
696x10-4m3
Volume of air displaced
= Volume of vapour
...
0 x 105) - (4
...
958 x 105 Nm-2
T1 = 303 K
Lab Values
V1 = 1
...
T
...
958 x 10-5 x 105 Nm-2
Po=1
...
958 x 105 x 1
...
013 x 105
38
V0 = 1
...
445 x 10-4m3 of vapour at S
...
P = 0
...
The mass of 2
...
T
...
24 x 10-2 x 0
...
445 x 10-4
The molecular mass of the substance = 122
...
46
= ______ = 61
...
Choose the best answer :
1
...
T
...
a) 22
...
8 L
c) 11
...
6 L
2
...
7g of iodine
...
The value of gram molecular volume of ozone at S
...
P is
a) 22
...
24 L
c) 11
...
2 L
4
...
5 gram- atoms of Nitrogen is same as
the atoms in
a) 12g of C
b) 32g of S
c) 8g of the oxygen
d) 24g of magnesium
...
The number of gram-atoms of oxygen in 128g of oxygen is
a) 4
b) 8
c) 128
d) 8x6
...
The total number of moles present in 111 g of CaCl2 is
a) One mole b) Two moles
c) Three moles d) Four moles
7
...
Which of the following contains same number of carbon atoms as are in
6
...
0g ethane b) 8
...
0g Propane d) 28
...
Which of the following contains maximum number of atoms?
a) 2
...
0g oxygen c) 2
...
0g methane
10
...
Which of the following pair of species have same number of atoms
under similar conditions ?
a) 1L each of SO2 and CO2 b) 2L each of O3 and O2
c) 1L each of NH3 and Cl2 d) 1L each of NH3 and 2L of SO2
12
...
0 g of oxygen contains number of atoms same as in
a) 4 g of S
b) 7 g of nitrogen
d) 12
...
5 g of H2
13
...
02 x 1024 CO molecules is
a) 1 gm-molecule
b) 0
...
Hydrogen phosphate of certain metal has a formula MHPO4, the
formula of metal chloride is
c) MCl2 d) MCl4
a) MCl
b) MCl3
15
...
mass
20)
...
Which of the following compound has / have percentage of carbon
same as that in ethylene (C2H4) ?
a) propene b) Cyclohexane c) Ethyne
d) Benzene
17
...
1 M solution of sodium Carbonate contains
b) 106 g of Na2CO3
a) 53 g of Na2CO3
d) 5 x 102 millimoles of Na2CO3
c) 10
...
Fill in the blanks
atoms
...
One mole of a triatomic gas contains
2
...
oxygen atoms
...
11
...
T
...
Equal volumes of different gases under similar conditions of
temperature and pressure contain equal number of
40
5
...
O atoms
...
7 g of CO contains
22
7
...
Match the following
Column A
1
...
Law of multiple
proportions
3
...
2 gm-equivalents of
Na2CO3
5
...
4 L at S
...
P
6
...
1 gm-atom of rhombic
sulphur
8
...
Mohr's Salt
Column B
a
...
106 g
6
...
d
...
f
...
01 moles of solute in one L of
solution
Liquid element
Calcium carbide
g
...
Fe(SO4)
...
i
...
Answer the following
1
...
2
...
What are the informations conveyed by a chemical equation ?
4
...
Fe + H2O → Fe3O4 + H2
ii
...
KMnO4 + H2SO4 → K2SO4 + MnSO4 + H2O + O2
iv
...
Molecular mass, Mole
41
concept, Avogardo number and its significance are dealt
...
By knowing the
percentage composition of elements in a compound, empirical formula and
molecular formula can be calculated
...
So, the method of
balancing the any equation explained and given or practice
...
References :
1
...
2
...
McMillan Indian Limited, Reprint-2002
...
Heinemann Advanced Science Chemistry – Second Edition
Ann and Patrick Fullick 2000
Heineman Educational
Publishers, Oxford
...
Inorganic Chemistry, P
...
Soni
...
GENERAL INTRODUCTION TO
METALLURGY
OBJECTIVES
•
Know the ores and minerals of elements
•
Learn the purification methods of ores
•
Understand the different metallurgical processes
•
Know the importance of purification of metals
•
Understand clearly the extraction of Cu, Au, Ag, Pb, Zn and Al
•
Gain knowledge about the mineral wealth of India and Tamilnadu
2
...
e
...
The earthy impurities such as sand, clay, rocks etc
...
Thus a large
number of metals in nature occur in the combined form along with other
elements, but some metals, such as Ag, Au, Pt etc
...
Ag occurs in native (or free) as
well as in the form of compounds
...
Thus a
mineral is a naturally occurring material present in earth’s crust which
contains metal in the native (or free state) or in combined state
...
When a mineral contains sufficient amount of a
metal in combined state, from which it can be readily and profitably
separated on commercial scale, then the mineral is said to be an ore of the
metal
...
A
mineral from which a metal can be profitably extracted is called an ore
...
Hence bauxite is an ore of
aluminium, while clay is a mineral
...
In the combined state ores are generally found in the form of oxides,
sulphides, carbonates, sulphates, chlorides and silicates
...
1
...
1 Classification of ores
Ore or
Composition
Mineral
Oxide ores Bauxite
Al2O3
...
FeS2
ores
Pyrites
Copper
Cu2S
Glance
Zinc Blende ZnS
Cinnabar
HgS
Galena
PbS
Argentite or Ag2S
Silver
Glance
Carbonate Magnesite MgCO3
ores
Ore
Dolomite
Calamine
Malachite
Limestone
CaCO3
...
Cu(OH)2
CaCO3
44
Metal
Present
Al
Cu
Fe
Zn
Sn
Mn
U
Cu
Cu
Zn
Hg
Pb
Ag
Mg
Mg
Zn
Cu
Ca
Halide ores Rock Salt
Na
KCl
...
6H2O
AgCl
KCl
3 NaF
...
7H2O
Mg
Ag
K
Al
Mg
CaSO4
...
3MgSiO3
Ca
Ba
Pb
Mg
Felspar
K2O
...
6SiO2 or
KAlSi3O8
Al
Mica
Sulphate
ores
NaCl
K2O
...
6SiO22H2O
Al
Carnallite
Horn Silver
Sylvine
Cryolite
Epsom Salt
Gypsum
Barytes
Anglesite
Silicate ores Asbestos
Phosphate
ores
Phosphorite Ca3(PO4)2
P
2
...
(a) Metals which are sufficiently unreactive to occur uncombined (ie in
elementary form) are present in group 10 and 11 of the 2nd and 3rd
transition series (e
...
(b) Metalloids (e
...
(c) The more strongly metallic elements that form positive ions readily
are found as oxides (transition metals), carbonates (group 2 metals) or
chlorides (group 1 metals)
...
All other
metals are found in combined state in the nature
...
1%), Si (26%),
Al(7
...
2%), Ca (3
...
4%), Mg (2
...
0%) by weight
...
(b)Carbonates-Na, Cu, Mg, Ca, Ba, Zn, Fe etc
...
Source from sea
Four elements such as Na, Mg, Cl2 and Br2 can be extracted from the
oceans or salt brines, where they are present as monoatomic ions (Na+,
Mg2+, Cl-, Br -)
...
2 represents the descending mass abundance of elements
...
A large
number of biomolecules contain metal ions ; many of these molecules are
proteins
...
Table 2
...
3 Purification of ores
The ore is generally associated with rock impurities like clay, sand
etc
...
The purification of ore means removal of
gangue from the powdered ore
...
Thus, the percentage of the ore
in the concentrated ore is higher than that in the original ore
...
(i) Gravity separation process or hydraulic washing
This method is especially suitable for heavy ‘oxide’ ores like
haematite, tinstone, etc
...
The lighter sandy, and earthy impurities are washed away; while
the heavier ore particles are left behind
...
This process is based on the fact that
the sulphide ore particles are only moistened by oil; while those of oxide,
and gangue particles are moistened only by water
...
The oil forms a foam (or froth) with air
...
2
...
The froth is skimmed off, collected,
and allowed to subside to get concentrated ore
...
2
...
g
...
The powdered ore (containing the associated magnetic
impurities) is made to fall (from a hopper) on a belt moving over
electromagnetic roller
...
2
...
Fig
...
2 Electromagnetic separation method
(iv) Chemical method
This method is employed in case where the ore is to be in a very
pureform, e
...
, aluminium extraction
...
When bauxite ore is
treated with NaOH, the Al2O3 goes into solution as sodium metaaluminate leaving behind the undissolved impurities [Fe2O3, SiO2,
Fe(OH)3,etc
...
Al 2 O 3 + 2 NaOH → 2 NaAlO + H 2 O
2
Sod
...
aluminate
(In solution form)
48
The filtrate (containing sodium meta-aluminate) on dilution, and
stirring gives a precipitate of aluminium hydroxide, which is filtered, and
ignited to get pure alumina
...
4 Metallurgical processes
Metallurgy is a branch of chemistry which deals with,
(i) Extraction of metals from ores
(ii) Refining of crude metal
(iii)Producing alloys and the study of their constitution, structure and
properties
...
The extraction of metals cannot be carried out by any universal
method because extraction of each metal requires different methods of
extraction
...
In
general, noble metals such as Au, Ag, etc are usually extracted by
electrolysis of their chlorides, oxides or hydroxides
...
g
...
, are extracted by making use of roasting and
smelting methods
...
4
...
In the process of roasting, the ore either alone or with the
addition of suitable material, is subjected to the action of heat in excess
of air at temperature below its melting point
...
During roasting
(a) Volatile impurities like S, As, Sb etc
...
Mass becomes
porous and thus it can easily be reduced
...
49
Oxidising Roasting – In this type of roasting S, As, and Sb impurities
are removed in the form of their volatile oxides as SO2, As2O3 and Sb2O3
etc
...
The ore is simultaneously
converted into its oxides
...
2ZnS + 3O2 → 2ZnO + 2SO2
2PbS + 3O2 → 2PbO + 2SO2
Calcination
Another method of conversion of ore into metal oxide (oxidation) is
called calcination
...
The process of calcination is carried out in the case of carbonate
and hydrated ore
...
(b) Gases may be expelled
...
(d) The
mass becomes porous
...
For example,
CaCO3 (limestone) → CaO + CO2 ↑
MgCO3 (Magnesite) → MgO + CO2 ↑
MgCO3
...
Cu(OH)2 (Malachite) → 2CuO + H2O + CO2 ↑
ZnCO3 (Calamine) → ZnO + CO2↑
2Fe2O3
...
Calcination is usually carried
out in reverberatory furnace
...
4
...
It is the process used for all operations where the
metal is separated by fusion from the ore
...
In general, the process of
separation of a metal or its sulphide mixture from its ore in fused state is
50
called smelting
...
In smelting, the roasted or calcined ore is mixed with coke and then
heated in a furnace
...
For
example, in the extraction of iron, haematite ore(Fe2O3) is smelted with
coke and limestone (flux)
...
Fe2O3 + 3C → 2Fe + 3CO
CaCO3 → CaO + CO2
Fe2O3 + 3CO → 2Fe + 3CO2
CaO + SiO2 → CaSiO3
Flux + Gangue → Slag
Similarly, in the extraction of copper from copper pyrites, the ore is
mixed with coke and heated in blast furnace (smelted)
...
A mixture containing
sulphide of copper and iron, called matte is formed in the molten state
...
4
...
Steel
is an alloy of carbon and iron and contains 0
...
5% of carbon with
traces of sulphur, phosphorus, manganese and silicon as impurities
...
15-0
...
3-0
...
8-1
...
The process was discovered by Henry Bessemer in England (1856)
...
51
This process mainly differs in the use of acidic and basic refractory
linings of the converters
...
09%) is treated by acidic Bessemer process and high phosphorus pig
iron (more than 1
...
The converter is a pear shaped furnace about 6m high and 3m in
diameter
...
If the impurities present in the pig iron are basic, e
...
,
manganese, a lining of silica brick is used and the process is known as
acid Bessemer process
...
g
...
, a basic lining of lime (CaO) or magnesia (MgO) is used
in the converter and process is then known as basic Bessemer process
...
The converter is mounted on shafts or trunnions, one of which is hollow
and serves as a wind pipe and upon which the converter can rotate in any
position
...
The molten pig iron is mixed in mixers and then charged into
converter
...
The
converter is first set in the horizontal position and after charging the
converter is adjusted in vertical position
...
The blast is continued for about 15 minutes during
which the impurities are oxidized
...
Carbon is also oxidized to CO
...
3
...
1
...
2
...
4
...
This method is applicable to many
metals such as Cu, Ag, Pb, Au, Ni, Sn, Zn etc
...
A
solution of a salt of the metal is taken as an electrolyte
...
By this process, more metal ions undergo
reduction and pure metal is deposited at the cathode
...
For example, in the refining of copper, impurities
like Fe and Zn dissolve in the electrolyte, while Au, Ag and Pt are left
behind as anode mud
...
Copper sulphate
solution is used as an electrolyte
...
Cu2+ + 2e- → Cu
2) Copper (of impure anode) forms copper ions, and these go into
solution of electrolyte
...
Impurities like zinc, iron, etc
...
, are left behind as anode mud
...
98% pure copper by electrolytic refining (Fig
...
4)
...
2
...
It is
based on the principle that melting point of a substance is lowered by the
presence of impurities
...
(Fig
...
5)
...
2
...
A circular heater fitted around this bar is slowly moved longitudinally
from one end to the other
...
In this way, the impurities are swept from one
end of the bar to the other
...
54
(c) Mond’s process
Thermal methods include methods as carbonyl method,
decomposition of hydrides etc
...
For example, in case of nickel, the
impure metal is heated with CO
...
The process is known as Mond’s process
...
) forms a volatile carbonyl,
Ni(CO)4, when CO is passed over it at 500C
...
Questions
A
...
2
...
4
...
6
...
B
...
2
...
4
...
6
...
8
...
Froth flotation process is suitable for concentrating …………… ores
...
Gangue + flux → ……………………
...
…………………… is used as a foaming agent
...
Define Metallurgy
...
55
9
...
What is meant by electrolytic refining? Give example
...
What is anode mud?
12
...
Explain briefly on the following
1
...
2
...
3
...
4
...
What is roasting ? Explain different types of roasting with suitable
example
...
What is smelting ? Explain the process with example
...
What is Zone refining ? Describe the principle involved in the
purification of the metal by this method
...
How nickel is extracted by Mond’s process? Write the various
reactions involved in the process
...
Write short note on mineral wealth of India
...
Give a brief account of the mineral wealth of Tamil Nadu
...
Engineering chemistry - P
...
Jain and Monika Jain Twelth Ed - 1999
...
Industrial chemistry - B
...
Sharma, Tenth Ed
...
3
...
P
...
4
...
56
3
...
•
Recognise the merits and demerits of Niels Bohr's model of an atom
...
•
Analyse the significance of quantum number
...
•
Understand the quantum designation of electron
...
•
Understand the stability of different orbitals and its application in
writing the electronic configuration
...
3
...
According to this
theory, all matter is composed of very small particles called atoms
...
Dalton’s ideas of the structure of matter
were born out by a considerable amount of subsequent experimental
evidences towards the end of the nineteenth century
...
The proton, a positively
charged particle, is present in the central part of the atom called nucleus
...
The neutron, a neutral particle, is also present in the nucleus of the atom
...
57
Thomson’s Model of atom
In 1904 Sir J
...
Thomson proposed the first definite theory as to the
internal structure of the atom
...
This model of atom could account the electrical neutrality of atom,
but it could not explain the results of gold foil scattering experiment
carried out by Rutherford
...
He bombarded a thin gold foil with
D VWUHDP RI IDVW PRYLQJ SRVLWLYHO\ FKDUJHG
...
Rutherford’s Nuclear model of a atom
This model resulted from conclusion drawn from experiments on the
scattering of alpha particles from a radio active source when the particles
were passed through thin sheets of metal foil
...
-particles
passed through the foil
...
-particles are deflected
...
The positive charge has to be concentrated in a very small
YROXPHWKDWUHSHOOHGDQGGHIOHFWHGWKHSRVLWLYHO\FKDUJHG
...
This very small portion of the atom was called nucleus by
Rutherford
...
The diameter of the atom is about 10-10 m while that of nucleus
is 10-15m
...
On the basis of above observations and conclusions, Rutherford
proposed the nuclear model of atom
...
(b) The positive charge of the nucleus is due to protons
...
This
neutral particle, called neutron, was discovered later on by Chadwick
in 1932
...
The total number of nucleons is termed as
mass number(A) of the atom
...
Thus,
Rutherford’s model of atom resembles the solar system in which the
sun plays the role of the nucleus and the planets that of revolving
electrons
...
Thus, the total positive charge of the nucleus exactly balances
the total negative charge in the atom making it electrically neutral
...
(e) Electrons and the nucleus are held together by electrostatic forces of
attraction
...
2 Defects of Rutherford’s model
According to Rutherford’s model, an atom consists of a positive
nucleus with the electrons moving around it in circular orbits
...
C
...
As a result of this, its
orbit should become smaller and smaller Fig
...
1
...
This means that atom
would collapse and thus Rutherford’s model failed to explain stability of
atoms
...
3
...
e
...
Therefore, this model failed to explain the existence of certain
definite lines in the hydrogen spectrum
...
The
important postulates are:
(1) The electrons revolve round the nucleus only in certain selected
circular paths called orbits
...
These are numbered as 1, 2, 3, 4 …
...
(starting from the
nucleus) are designated as K, L, M, N …
...
(Fig
...
2)
...
This means that energy of an electron in a particular path
remains constant
...
(3) Only those orbits are permitted in which angular momentum of the
HOHFWURQ LV D ZKROH QXPEHU PXOWLSOH RI Ki ZKHUH µK¶ LV 3ODQFN¶V
constant
...
60
(4) If an electron jumps from one stationary state to another, it will
absorb or emit radiation of a definite frequency giving a spectral line
of that frequency which depends upon the initial and final levels
...
Fig
...
2 Bohr's orbits
Limitation of Bohr’s Theory
(i) According to Bohr, the radiation results when an electron jumps from
one energy orbit to another energy orbit, but how this radiation
occurs is not explained by Bohr
...
At that
time this was exactly what had been observed
...
Thus for example, the single H∞-spectral line of Balmer
series consists of many lines very close to each other
...
This would require the existence of new quantum numbers
...
g
...
), it
can not explain the spectral series for the atoms having a large
number of electrons
...
e
...
(vi) Bohr assumes that an electron in an atom is located at a definite
distance from the nucleus and is revolving round it with definite
velocity, i
...
it is associated with a fixed value of momentum
...
(vii) No explanation for Zeeman effect: If a substance which gives a line
emission spectrum, is placed in a magnetic field, the lines of the
spectrum get split up into a number of closely spaced lines
...
Bohr’s theory has no
explanation for this effect
...
This phenomenon is
known as Stark effect
...
3
...
In an atom a large number of electron
orbitals are permissible
...
These orbitals are
designated by a set of numbers known as quantum numbers
...
1
...
Each shell is characterized by a quantum
62
number called principal quantum number
...
The first level is also
known as K level
...
The first or K level is the orbit nearest to the nucleus and next
one is second or L level and so on
...
The subsidiary or azimuthal quantum number (l)
According to Sommerfield, the electron in any particular energy level
could have circular path or a variety of elliptical paths about the nucleus
resulting in slight differences in orbital shapes with slightly differing
energies due to the differences in the attraction exerted by the nucleus on
the electron
...
This is
denoted by the letter ’l’ and have values from 0 to n-1
...
n=2, l=0 and 1 ( 2 values or 2 sub- levels) s and p level
...
n=4, l=0, 1, 2 and 3 (4 values or 4 sub-levels) s, p ,d and f level
...
Magnetic quantum number (m)
In a strong magnetic field a sub-shell is resolved into different
orientations in space
...
This explains the appearance of additional lines in
atomic spectra produced when atoms emit light in magnetic field
...
The values are -‘l’ through zero to +‘l’ and
thus there are (2l+1) values
...
The three quantum numbers labeling an atomic orbital can be used
equally well to label electron in the orbital
...
4
...
Therefore the spin quantum number can
have only two values +1/2 or –1/2
...
To sum up, the four quantum numbers provide the following
informations:
1
...
2
...
l identifies the subshell and
determines the shape of the orbital
...
e
...
To some extent l also determines the
energy of the orbital in a multi-electron atom
...
ml designates the orientation of the orbital
...
It
means that the number of orbitals is equal to the number of ways in
which they are oriented
...
ms refers to orientation of the spin of the electron
...
Thus, there is one 3s
orbital (n = 3, l = 0 and ml = 0); there are three p orbitals (n = 3, l = 1 and
ml = -1, 0, 1) there are five 3d orbitals (n = 3, l = 2, ml = -2, -1, 0, 1, 2)
...
64
Example 2
Using s, p, d, f notations, describe the orbital with the following
quantum numbers (a) n=2, l = 1 (b) n = 4, l = 0 (c) n = 5, l = 3 (d) n = 3,
l = 2
...
4 Shapes or boundary surfaces of Orbitals
s-orbitals: For s-orbital l = 0 and hence, m can have only one value,
i
...
,
m = 0
...
In other
words s-orbitals are spherically symmetrical
...
The s-orbitals of
higher energy levels are also spherically symmetrical
...
These are called nodes
...
In the ns orbital, number of nodes are (n-1)
...
This means that there are three possible orientations of
electron cloud in a p-sub-shell
...
Each p-orbital has two lobes, which are separated by a
point of zero probability called node
...
In the absence of magnetic field these three p-orbitals are equivalent
in energy and are, therefore, said to be three-fold degenerate or triply
degenerate
...
This probably accounts for the splitting of a
single spectral line into a number of closely spaced lines in presence of a
magnetic field (fine structure)
...
e
...
All these five orbitals, in the absence
of magnetic field, are equivalent in energy and are, therefore, said to be
five-fold degenerate
The three orbitals namely dxy, dyz and dzx have their lobes lying
symmetrically between the coordinate axes indicated in the subscript to
d, e
...
the lobes of dxy orbital are lying between the x-and y-axes
...
dx2-y2 and dz2 orbitals have their
lobes along the axes (i
...
along the axial directions), e
...
, the lobes of
d
orbital lie along the x and y-axes, while those of dz2 orbital lie along
the z-axis
...
3
...
The distribution of quantum numbers among the electrons in a given
atom is governed by Pauli’s Exclusion principle, which states that “it is
impossible for any two electrons in a given atom to have all the four
quantum numbers identical” i
...
, in an atom, two electrons can have
maximum three quantum numbers (n, l and m) the same and the fourth
(s) will definitely be having a different value
...
In other words
the two electrons in the same orbital should have opposite spins ( ↑↓ )
...
Let us
illustrate this point by considering K and L shells
...
For n = 1, l = 0 and m = 0
...
The different values of n, l, m and s
66
given above give the following two combinations of the four
quantum numbers, keeping in view the exclusion principle
...
(i) n = 1, l = 0, m = 0
s = +1/2 (1st electron)
(ii) n = 1, l = 0, m = 0,
s = -1/2 (2nd electron)
(Two electrons in l = 0 sub-shell i
...
, 1s-orbital)
These two combinations show that in K shell there is only one subshell corresponding to l = 0 value (s-sub-shell) contains only two
electrons with opposite spins
...
For n = 2 the different values of l, m
and s give the following eight combinations of four quantum
numbers
...
e
...
67
3
...
Pairing of electrons requires
energy
...
This is known as Hund’s rule of maximum
multiplicity
...
1)
...
1 Representation of arrangements of electrons
Atomic
Number of
Number Element 1s 2s 2px 2py 2pz unpaired
electrons
1
2
3
4
H
He
Li
Be
9
9;
9; 9
9; 9;
5
B
9; 9; 9
9
1
6
7
8
C
N
O
9; 9; 9
9; 9; 9
9; 9; 9;
9
9
9
9
9
2
3
2
9
10
F
Ne
9; 9; 9; 9; 9
9; 9; 9; 9; 9;
1
0
1
0
1
0
Thus, if three electrons are to be filled in the p- level of any shell, one
each will go into each of the three (px, py, pz) orbitals
...
The
unpaired electrons play an important part in the formation of bonds
...
7 Aufbau Principle
The word ‘aufbau’ in German means ‘building up’
...
The principles
states: In the ground state of the atoms, the orbitals are filled in
68
order of their increasing energies
...
The order
in which the energies of the orbitals increase and hence the order in
which the orbitals are filled is as follows:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s……………
...
3
...
Starting from the top, the direction of the arrows gives the order of filling
of orbitals
...
If two orbitals have the same (n+1) value, the orbital with
lower value of n has the lower energy
...
3
...
However in hydrogen
atom, they have the same energy
...
8 Stability of orbitals
According to Hund’s rule atoms having half-filled or completelyfilled orbitals are comparatively more stable and hence more energy is
69
needed to remove an electron from such atoms
...
The extraordinary stability of half-filled and completely filled
electron configuration can be explained in terms of symmetry and
exchange energy
...
Moreover, in such configuration electron can
exchange their positions among themselves to maximum extent
...
Element Atomic Electronic configuration
Number
in the ground state
N
7
1s2 2s2 2px1 2py1 2p1z
Ne
Symmetrical
distribution
of electrons
10
1s2 2s2 2px2 2py2 2p2z
Thus the p3,p6,d5,d10,f7 and f14 configuration which are either
completely filled or exactly half-filled are more stable
...
Therefore, to acquire more stability one of the 4s electron goes
into 3d orbitals so that 3d orbitals get half-filled or completely filled in
chromium and copper respectively
...
Choose the best answer
1
...
2
...
The statement is known as
(a) Exclusion principle
(c) Hund’s rule
(e) Newlands law
...
When the 3d orbital is complete, the new electron will enter the
(a) 4p orbital (b) 4f orbital (c) 4s orbital
(d) 4d orbital (e) 5s orbital
...
The preference of three unpaired electrons in the nitrogen atom can
be explained by : (a) Pauling’s exclusion principle (b) Aufbau
principle (c) Uncertainty principle (d) Hund’s rule (e) None of these
...
The number of orbitals in a p-sub-shell is
(a) 1 (b) 2 (c) 3 (d) 6 (e) 5
...
The nucleus of an atom contains :
(a) Electrons and protons (b) Neutrons and protons
(c) Electrons, protons and neutrons (d) Neutrons and electrons
(e) None of these
...
Which is the lightest among the following? (a) An atom of hydrogen
(b) An electron (c) A neutron (d) A proton (e) An alpha particle
...
Which of the following has no neutrons in the nucleus? (a) Deuterium
(b) Helium (c) Hydrogen (d) Tritium (e) An alpha particle
...
When the value of the azimuthal quantum number is 3, the magnetic
quantum number can have values :
(a) +1,-1 (b) +1,0, 1 (c) +2,+1,0, -1,-2
(d) +3,+2, +1,0, -1,-2,-3 (e) +3,-3
...
2p orbitals have :
(a) n = 1,l = 2 (b) n=1, l = 0 (c) n = 2, l = 0
(d) n = 2, l =1 (e) n =1, l =1
...
The atomic number of an element is 17 and its mass number is 37
...
12
...
13
...
B
...
The decomposition of an electrolyte by passage of electricity is
known as ………………
...
When cathode rays are focused on thin metal foil, it gets heated up to
……………
3
...
4
...
5
...
72
were
C
...
What is the charge of an electron, proton and a neutron ?
2
...
What is the maximum number of electrons that an orbital can have?
4
...
Sketch the shape of s and p-orbital indicating the angular distribution
of electrons
...
What are the charge and mass of an electron?
7
...
Give the order of filling of electrons in the following orbitals 3p,
3d,4p, 3d and 6s
...
What is meant by principal quantum number?
10
...
What are the particles generally present in the nuclei of atoms?
12
...
Show how the atom of the element is constituted?
13
...
What is the principal defect of Bohr atom model?
15
...
16
...
What are the possible values of l ?
17
...
What are the possible values of m?
18
...
(Z=24)
...
Which energy level does not have p-orbital?
73
20
...
What is the total number of
p-orbital?
21
...
Write the values of l and m for p-orbitals
...
Which quantum accounts for the orientation of the electron orbital?
24
...
Give the values for all quantum numbers for 2p electrons in nitrogen
(Z = 7)
...
Give the electronic configuration of Mn2+ and Cu
...
27
...
Explain briefly on the following
1
...
Explain its significance in the electronic
build up of atoms
...
Using the s, p, d, notation, describe the orbital with the following
quantum numbers? (a) n = 1, l=0; (b) n = 2,l = 0; (c) n = 3, l = 1;
(d) n = 4, l =3
...
Using the a Aufbau principle, write the electronic configuration in the
ground state of the following atoms : Boron (Z = 5 ) Neon (Z = 10)
and Aluminium (Z = 13)
...
What is Rutherford’s α- ray scattering experiment? What are its
conclusions?
5
...
Explain the various quantum numbers which completely specify the
electron of an atom
...
74
•
Niel's Bohr model and sommerfield's extension were mentioned with
diagrammatic representation
...
•
Occupancy of electrons following Hund's rule Aufbau principle,
Pauli's exclusion principle are explained with represnetation
...
D
...
2) Theoretical Inorganic chemistry - M
...
Day and J
...
1985
...
S
...
4) Selected topics in Inorganic Chemistry - U
...
D
...
D
...
- 1993c
...
PERIODIC CLASSIFICATION-I
OBJECTIVES
•
Recall the history of periodic classification
...
•
Understand the electronic configuration of the elements and the
classification based on it
...
•
Know the anamolous periodic properties of elements and to reason it
...
1 Brief history of periodic classification
More than one hundred and nine elements are known today,
...
It would be difficult to study individually the chemistry of all
the elements and their numerous compounds
...
This gave rise to the necessity of
classifying the elements into various groups or families having similar
properties
...
Periodic table may be defined as the arrangements of various
elements according to their properties in a tabular form
...
Several chemists have for long tried to classify the elements
and to find patterns in their properties
...
These groups were called
triads
...
For example lithium, sodium and potassium constituted
one triad
...
Table 4
...
5
Na
23
Sr
88
Br
80
K
39
Ba
137
I
127
Newlands Law of Octaves
In 1865, John Newlands (English Chemist) observed that if the
elements were arranged in order of their increasing atomic weights, the
eighth element starting from a given one, possessed properties similar to
the first, like the eighth note in an octave of music
...
It worked well for the lighter elements but failed when applied
to heavier elements
...
Lother-Meyer in Germany gave a more detailed and
accurate relationship among the elements
...
He
pointed out that elements occupying similar positions in the curve
possessed similar properties
...
He gave his famous scheme of the periodic classification
of elements known as the periodic law
...
It means that when elements are arranged in order of increasing
atomic weights, the elements was similar properties recur after regular
intervals
...
Mendeleev, while studying
his Periodic Table had found that in certain cases the regularity in
behaviour between two succeeding elements was not observed
...
Mendeleev
named these elements as eka-aluminium and eka-silicon because he
believed that they would be similar to aluminium and silicon
respectively
...
The discoveries / synthesis of new
elements have continued even to the present day, raising their number to
120
...
e
...
The rest known as transuranium elements have been
synthesized in the laboratories, which are highly unstable
...
The modified periodic table is essentially similar to that of
Mendeleev with a separate column added for noble gases, which were
not discovered until the closing years of the nineteenth century
...
The Mendeleev’s modified periodic table consists of:
(1) Nine vertical columns called groups
...
(The members of zero group were not discovered at the
time of Mendeleev)
...
Group VIII consists of three sets,
each one containing three elements
...
(2) Seven horizontal rows, called periods
...
First period contains two elements
...
These periods are called short periods
...
These periods are called long
periods
...
Seventh period is incomplete and contains nineteen elements
according to early classification
...
2 IUPAC periodic table and IUPAC nomenclature of elements with
atomic number greater than 100
Modern Periodic Law
In 1913, a British Physicist Henry Moseley showed that the atomic
number is a more fundamental property of an element than its atomic
weight
...
The modern periodic law states that “ the physical and chemical
properties of the elements are periodic function of their atomic numbers
...
The periodic repetition is called periodicity
...
Thus, if the arrangement
of electrons in the outermost shell (valence shell) of the atoms is the
same, their properties will also be similar
...
Similar behaviour of alkali metals is attributed to the similar valence
shell configuration of their atoms
...
Thus we find that the periodic
repetition of properties is due to the recurrence of similar valence shell
configuration after certain intervals
...
Long form of the Periodic Table: The periodic table is constructed
on the basis of repeating electronic configurations of the atoms when
they are arranged in the order of increasing atomic numbers
...
Readers are advised to follow the periodic table closely while studying
the structural features of the long form of the Periodic Table
...
Periods: In terms of electronic structure of the atom, a period
constitutes a series of elements whose atoms have the same number of
electron shell i
...
, principal quantum number (n)
...
The first period corresponds to the filling of electrons in the first
energy shell (n = 1)
...
This means that there can
be only two elements (hydrogen, 1s1 and helium, 1s2 ) in the first period
...
Since there are only four orbitals (one 2sand three 2p- orbitals) to be filled, it can accommodate eight electrons
...
It starts with lithium (Z = 3)
in which one electron enters the 2s-orbital
...
The third period begins with the electrons entering the third energy
shell (n = 3)
...
As such only four orbitals (one 3s and three 3p)
corresponding to n = 3 are filled before fourth energy level begins to be
filled
...
The fourth period corresponding to n = 4 involves the filling of one
4s and three 4p-orbitals (4d and 4f orbitals have higher energy than 5sorbital and are filled later)
...
Thus,
altogether nine orbitals (one 4s, five 3d and three 4p ) are to be filled and
therefore, there are eighteen elements in fourth period from potassium
(Z = 19) to krypton (Z = 36)
...
The fifth period beginning with 5s-orbital (n=5) is similar to fourth
period
...
80
The sixth period starts with the filling of 6s-orbitals (n= 6)
...
As such there
are thirty two elements in sixth period starting from cesium (Z = 55) and
ending with radon (Z = 86)
...
It constitutes the first finner transition series which is called lanthanide series
...
It would also have
contained 32 elements corresponding to the filling of sixteen orbitals
(one 7s, seven 5f, five 6d and three 7p), but it is still incomplete
...
The filling up of 5f- orbitals begins
with thorium (Z = 90) and ends up at lawrencium (Z = 103)
...
It mostly
includes man made radioactive elements
...
The number of elements and the corresponding orbitals being filled
are given below
...
2
Period
Principal
Valence
shell (=n)
Orbitals
being filled
up
Electrons to
Number of
be accommoelectrons
dated
First
N=1
1s
2
2
Second
N=2
2s, 2p
2+6
8
Third
n=3
3s, 3p
2+6
8
Fourth
n=4
4s, 3d, 4p
2 +10+6
18
Fifth
n=5
5s, 4d, 5p
2+10+6
18
Sixth
n=6
6s, 4f, 5d, 6p
2+14+10+6
32
Seventh
n=7
7s, 5f, 6d, 7p
2+14+10+6
32
81
The first three periods containing 2, 8 and 8 elements respectively are
called short periods, the next three periods containing 18, 18 and 32
elements respectively are called long periods
...
A group
consists of a series of elements having similar configuration of the outer
energy shell
...
According to the recommendations of the International
Union of Pure and Applied Chemistry (IUPAC), these groups are
numbered from 1 to 18
...
The elements belonging to the
same group are said to constitute a family
...
IUPAC Nomenclature for Elements with Z > 100
The elements beyond uranium (Z = 92) are all synthetic elements and
are known as transuranium elements
...
These elements fermium (Z = 100),
mendelevium (Z = 101), nobelium (Z = 102) and lawrencium (Z = 103)
are named after the names of famous scientists
...
Also some of these elements have been
assigned two names/symbols
...
But the following elements have been assigned only one official
name
...
To
overcome all these difficulties, IUPAC nomenclature has been
recommended for all the elements with Z > 100
...
The names of these elements are
derived from their numerical roots
...
3
Atomic
number
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
Name of the
element
Unnilunnium
Unnilbium
Unniltrium
Unnilquadium
Unnilpentium
Unnilhexium
Unnilseptium
Unniloctium
Unnilennium
Ununnilium
Unununium
Ununbium
Ununtrium
Ununquadium
Ununpentium
Ununhexium
Ununseptium
Ununoctium
Ununennium
Unbinilium
83
Symbol
Unu
Unb
Unt
Unq
Unp
Unh
Uns
Uno
Une
Uun
Uuu
Uub
Uut
Uuq
Uup
Uuh
Uus
Uuo
Uue
Ubn
84
4
...
We have already
learnt that an electron in an atom is characterized by a set of four
quantum numbers and the principal quantum number (n) defines the main
energy level known as the Shell
...
(a) Electronic Configuration in periods
Each successive period in the periodic table is associated with the
filling up of the next higher principal energy level (n=1, n=2,etc
...
The first period starts with the filling of the lowest level (1s) and
has thus the two elements-hydrogen (1s1) and helium (1s2) when the first
shell (K) is completed
...
The next element, beryllium has four
electrons and has the electronic configuration 1s22s2
...
Thus there are 8 elements in the
second period
...
Successive filling of 3s and 3p orbitals gives
rise to the third period of 8 elements from sodium to argon
...
Now you may note that before the 4p orbital is filled, filling up
of 3d orbitals becomes energetically favourable and we come across the
so-called 3d Transition Series of elements
...
Altogether we have 18
elements in this fourth period
...
This period ends at xenon with filling
up of the 5p orbitals
...
Filling
up of the 4f orbitals begins with cerium (Z=58) and ends at lutetium
(Z=71) to give the 4f-inner transition series, which is called the
Lanthanoid Series
...
This period will
end at the element with atomic number 118 which would belong to the
noble gas family
...
The 4f- and
5f- transition series of elements are placed separately in the periodic table
to maintain its structure and to preserve the principle of classification by
keeping elements with similar properties in a single column
...
Group 1 (the alkali metals) is an
example
...
4)
...
4 Types of elements : Electronic configuration of alkali
metals
Atomic
Symbol
number
Electronic configuration
3
Li
1s22s1 or [He] 2s1
11
Na
1s22s22p63s1 or [Ne] 3s1
19
K
1s22s22p63s2 3p64s1or [Ar] 4s1
37
Rb
1s22s22p63s2 3p64s2 3d104p65s1 or
[Kr] 5s1
55
Cs
1s22s22p63s2 3p64s2 3d104p65s2
4d105p66s1 or [Xe] 6s1
Types of elements: s-, p-,d-, f- Blocks
The aufbau principle and the electronic configuration of atoms
provide a theoretical foundation for the periodic classification
...
Strictly, helium belongs
to the s-block but its positioning in the p-block along with other group 18
elements is justified because it has a completely filled valence shell (1s2)
and as a result, exhibits properties characteristic of other noble gases
...
It has a lone s- electron and hence can
be placed in group 1 (alkali metals)
...
Because it is a special case, we
shall place hydrogen separately at the top of the Periodic Table
...
s-Block Elements
The elements of group 1 (alkali metals) and group 2 (alkaline earth
metals) which have ns1 and ns2 outermost electronic configuration belong
to the s-block elements
...
They lose the outermost electron(s) readily to form 1+ (in the
case of alkali metal) or 2+ ions (in the case of alkaline earth metals)
...
The compounds of the s-block elements, with the exception of those of
beryllium are predominantly ionic
...
The outermost electronic
configuration varies from ns2np1 to ns2np6 in each period
...
All the
orbitals in the valence shell of the noble gases are completely filled by
electrons and it is very difficult to alter this stable arrangement by the
addition or removal of electrons
...
Preceding the noble gas family are two chemically
important groups of nonmetals
...
These two groups of elements have higher
negative electron gain enthalpies and readily add one or two electrons
respectively to attain the stable noble gas configuration
...
The d-block Elements (Transition Elements)
These are the elements of group 3 to 12 in the center of the periodic
table
...
These
elements have the outer electronic configuration (n-1) d1-10 ns1-2
...
They mostly form colored ions and exhibit variable
valency
...
90Th-103Lr are characterized
by the outer electronic configuration (n-2) f1-14 (n-1) d0-10ns2
...
These two series of
elements are hence called the inner transition elements (f-Block
Elements)
...
The chemistry of the early actinoids is more
complicated than the corresponding lanthanoids, due to the large number
of oxidation states possible for these actinoid elements
...
Many of the actinoid elements have been made
only in nanogram quantities or less by nuclear reactions and their
chemistry is not fully studied
...
Example 1
The elements Z=117 and 120 have not yet been discovered
...
Solution
We see from the periodic table that element with Z=117, would
belong to the halogen family (group 17) and the electronic configuration
88
would be
...
the element with Z=120, will be placed
in group 2 (alkaline earth metals), and will have the electronic
configuration [Uuo]8s2
...
The elements can be divided into
Metals and Non-metals
...
Metals are
usually solids at room temperature (Mercury is an exception); they have
high melting and boiling points
...
They are malleable (can be flattened into thin sheets by
hammering) and ductile (can be drawn into wires)
...
Nonmetals are usually solids or gases at room temperature with low melting
and boiling points
...
Most non-metallic solids are brittle and are neither malleable nor ductile
...
The change form metallic to non-metallic character is
not abrupt as shown by the thick zig-zag line in the periodic table
...
g
...
These elements are called Semi Metals or Metalloids
...
Solution
Metallic character increases down a group and decreases along a
period as we move from left to right
...
4
...
The periodicity is due to similar electronic
89
configuration of outer-most shells
...
(i) Atomic and ionic radii
The size of an atom can be visualized from its atomic radius
...
For example, the atomic radius of hydrogen atom is equal to 74/2
pm = 37 (bond distance in hydrogen molecule (H2) is 74pm)
...
g
...
Explanations
We know that as we proceed from left to right in a period, the
electrons are added to the orbitals of the same main energy level
...
But with the addition of each electron, the nuclear
charge (i
...
atomic number) increases by one
...
90
Table 4
...
4
...
g
...
This effect decreases the electrostatic attraction between the
nucleus and the valence-shell electrons and this decreased electrostatic
attraction increases the atomic and ionic radii
...
6 Atomic Radii / pm Down the Group Across a Family
Atom
Atomic
radius
Atom
Atomic
radius
Li
152
F
72
Na
186
Cl
99
K
231
Br
114
Rb
244
I
133
Cs
262
At
140
Fig
...
2 Variation of atomic radius with atomic number for alkali
metals and halogens
92
When we find some atoms and ions, which contain the same number
of electrons, we call them isoelectronic
...
Their radii would be
different because of their different nuclear charges
...
Anions with the greater
negative charge will have the larger radius
...
Example
Which of the following species will have the largest and the smallest
size Mg, Mg2+, Al, Al3+?
...
Cations are smaller than their
parent atoms
...
Hence the largest species is Mg; the smallest one is Al3+
The size of an anion greater while that of the cation is smaller than
that of its parent atom, e
...
F- (=1
...
72 Å); Cl-(=1
...
99Å); Na+(=0
...
90Å); Ca2+(=0
...
97Å)
...
The reason of the fact
that Na+ ion is smaller than Na atom is that Na+ ion has 10 electrons
(Na+→1s2,2s2p6) while Na atom has 11electrons (Na →1s2,2s2p6,3s1)
...
e
...
This nuclear charge of +11 can pull
10 electrons of Na+ ion inward more effectively than it can pull a greater
number of 11 electrons of Na atom
...
The reason why Cl- ion is bigger than Cl atom can also be explained
on a similar basis
...
The nuclear
charge in each case is +17, which cannot pull 18 electrons of Cl- ion as
effectively as it can pull 17 electrons of Cl atom inward
...
93
(ii) Ionization Energy: (Ionization Potential)
In modern terminology, ionization energy is known as ionization
enthalpy
...
The first ionization enthalpy may be
defined as the amount of energy required to remove the most loosely
bound electron from the isolated gaseous atom
...
It is expressed in terms of either
kJ/mol or electron Volts/atom
...
Li+ (g) + 7297 kJ mol-1 → Li2+ + eSimilarly the third ionization enthalpy will be higher than the second
and so on
...
4
...
Fig
...
3 Variation of first ionization analysis with atomic number for
elements with Z = 1 to 60
94
Variation of Ionization Energy in the periodic Table
It is seen from the Fig
...
4 that the ionization enthalpy of an element
depends on its electronic configuration
...
The high values of noble gases are due to completely filled
electronic configurations in their outermost shells and the low values of
alkali metals are due to their large size and a single electron in the
outermost shell
...
This
trend can be explained in terms of increase in nuclear charge and
decrease in size from left to right in a period
...
As we
move down the group, the outer electrons, which are to be removed, are
farther from the nucleus and there is an increasing screening of the
nuclear charge by the electrons in the inner shells
...
Fig
...
4 (a) First ionization enthalpies of elements of the second
period as a function of atomic number (b) First ionization enthalpies
of alkali metals as a function of atomic number
Factors Influencing Ionization Enthalpy
The ionization enthalpy of an atom depends on the following factors
...
e
...
Thus, it becomes easier to remove an outermost
electron
...
(ii) Charge on the nucleus
Ionization enthalpy increases with increase in nuclear charge because
of the increase in the attractive force between the nucleus and the
electron
...
This is because when the inner electron shells
increases, the attraction between the nucleus and the outermost electron
decreases
...
Since the
penetration power of s-electron towards the nucleus is more, it will be
closer to the nucleus and will be held firmly
...
(v) Effect of half-filled and completely filled sub-levels
If an atom has half-filled or completely filled sub-levels, its
ionization enthalpy is higher than that expected normally from its
position in the periodic table
...
(iii)Electron affinity
In modern terminology, electron affinity is known as the electron
gain enthalpy
...
Atom (g) + Electron → Anion (g) + energy
96
Example, Cl (g) + e-→ Cl- (g) + EA
If an atom has high tendency to accept an electron, large energy will
be released
...
On the
other hand if an atom has less tendency to accept the electron small
amount of energy will be released, leading to small value of electron gain
enthalpy
...
For example,
electron gain enthalpy of
F = 322 kJ mol-1
Cl = 349 kJ mol-1
Br = 324 kJ mol-1 and
I
=295 kJ mol-1
Halogens (elements of group 17) can take up an electron to acquire
the stable noble gas configuration
...
Electron gain enthalpy values for the halogens are as
in Fig
...
5
...
This is expected on account of the increase in size of atoms, the
effective nuclear attraction for electrons decreases
...
Fig
...
5 Electron affinity enthalpies of halogens
97
From the electron gain enthalpy data of halogens it is clear that,
contrary to expectation, the electron gain enthalpy of fluorine is lower
than that of chlorine
...
The compactness of the
fluorine shell results in electron repulsion whenever an electron is
introduced into its 2p-orbital
...
In Cl atom, 3p-orbitals are not as compact
as the 2p-orbitals in fluorine atom
...
The electron gain enthalpy of chlorine is, therefore,
higher than that of fluorine
...
No more electrons can be accommodated in these orbitals
...
Their electron
gain enthalpies are zero
...
This is due to the increase in the nuclear charge,
which results in greater attraction for electrons
...
For example:
O- (g) + e- → O2- (g)
Since a negative ion O- and an electron repel each other, energy is
required and not released by the process
...
Factors influencing the magnitude of electron affinity
The magnitude of EA is influenced by a number of factors such as
(i) Atomic size; (ii) Effective nuclear charge; and (iii) Screening effect by
inner electrons
...
Explain your answer
...
Within a group, electron gain
enthalpy becomes less negative down a group
...
Hence the element with most negative
electron gain enthalpy is chlorine; the one with the least negative electron
gain enthalpy is phosphorus
...
The main
factors, which the electronegativity depends, are effective nuclear charge
and atomic radius
...
Smaller the atomic radius greater is the
electronegativity
...
This is due to the reason that the nuclear charge increases whereas atomic
radius decreases as we move from left to right in a period
...
In a group electronegativity decreases on moving down the group
...
Among halogens
fluorine has the highest electronegativity
...
0 (Pauling’s scale)
whereas cesium is the least electronegative element (E
...
= 0
...
In other words, cesium
is the most electropositive element and hence is the most metallic
element in the periodic table
...
of electrons
...
It is a number and has no units
...
It is the property of an
An atom has a relative value of
isolated atom
...
For example, spvalue of electron gain hybridized
carbon
is
more
enthalpy
...
It does not change regularly
It changes regularly in a period or a
in a period or group
...
Electronegativity of an element is important in determining the bond
character
...
Between the extremes the purely
covalent bond and purely ionic, the bonds will have different degrees of
ionic character
...
7 in
electronegativities, the bond has 50% ionic character
...
7, the bond is considered covalent, and greater than 1
...
100
Table 4
...
0
Be
F
1
...
0
B
2
...
5
Na
0
...
0
K
Br
0
...
8
Rb
0
...
5
Cs
0
...
1
O
3
...
5
Cl
I
4
...
According to Hund’s rule atoms having half-filled or completely
filled orbitals are comparatively more stable and hence more energy is
needed to remove an electron from such atoms
...
Example
A few irregularities that are seen in the increasing values of
ionization potential along a period can be explained on the basis of the
concept of half-filled and completely filled orbitals, e
...
, Be and N in the
second period and Mg and P in the third period have slightly higher
values of ionization potentials than those normally expected
...
Another example for irregularity in Ionization potential is observed in
the case of B and Be
...
3 eV, Be = 9
...
[Be (2s2) → Be+(2s1) +e-]
...
This
exception occurs in the case of those elements whose atomic numbers are
greater than 72
...
Table 4
...
8
Tc43
VIII
II B III A IV A
Ru44 Rh45 Pd46 Ag47 Cd48 In49
7
...
2
7
...
4
Ta73 W74
Re75
7
...
8
7
...
7
7
...
7
9
...
4
8
...
2
7
...
2
8
...
4
6
...
e
...
,Sn → Pb) shown by the elements
from Ta73 to Pb82 is due to the lanthanide contraction as a result of which
there occurs an increase in the nuclear charge without a corresponding
increase in size through the rare earths
...
Periodic Variations
Similarly in moving down a group electron affinity values generally
decrease, e
...
ECl>EBr>EI
...
102
Exceptions
There are, however, some exceptions to this general rule as is evident
from the following examples:
It is known that EF < ECl (EF = 322 kJ mol-1 , ECl = 349 kJ mol-1)
...
In period, electron affinity values generally increase on moving from
left to right in a period in the periodic table
...
g
...
Since Be and Mg
have completely filled s-orbitals (Be → 2s2, Mg → 3s2), the additional
electron will be entering the 2p-orbital in case of Be and 3p-orbital in
case of Mg which are of considerably higher energy than the 2s-and 3s
orbitals respectively
...
Choose the Best Answer
1
...
Representative elements are those which belong to :
(a) s and d-blocks (b) s and p-blocks (c) p and d-blocks
(d) d and f-blocks
3
...
Which of the following forms stable gaseous negative ion
...
The elements having highest ionization energies within their periods
are called :
(a) Halogens (b) Noble gases (c) Alkali metals
(d) Transition elements
103
6
...
7
...
8
...
The law of octaves was stated by : (a) Dobereiner (b) Mendeleev
(c) Moseley (d) Newland
10
...
Which of the following has the lowest melting point ?
(a) CsCl (b) RbCl (c) KCl (d) NaCl (e) LiCl
...
Which of the following hydroxide is most basic ?
(a) Mg (OH)2 (b) Ba (OH)2 (c) Ca(OH)2 (d) Be (OH)2
13
...
Which one among the following species has the largest atomic radius:
(a) Na (b) Mg (c) Al (d) Si
15
...
Which of the following has highest ionization potential?
(a) Sodium (b) Magnesium (c) Carbon (d) Fluorine
17
...
18
...
104
19
...
20
...
Which arrangement of the following set of atoms is in order of
increasing atomic radius: Na, Rb, K and Mg ;
(a) Na, Mg, K, Rb (b) Na, K, Mg, Rb (c) Mg, Na, K, Rb
(d) Na, Mg, Rb, K
22
...
Characteristic of transition elements is incomplete in : (a) d-orbitals
(b)f-orbitals (c) p-orbitals (d) s-orbitals
24
...
Which of the following atoms is likely to give off more energy on
gaining an electron ? (a) Na (b) Mg (c) Al (d) Cl
26
...
In the first transition series the incoming electron enters the :
(a) 4d-orbital (b) 3d-orbital (c) 5d-orbital (d) 6d-orbital
B
...
Mendeleev’s periodic law states that the properties of the elements
are the periodic functions of the ………………
2
...
3
...
of the atoms when they are
arranged in the order of increasing atomic numbers
...
The first three periods containing 2, 8 and 8 elements respectively are
called ……………
5
...
Minus
the number of outermost electrons
...
Write in one or two sentence
1
...
2
...
3
...
4
...
5
...
Which of the following pairs of elements would you expect to have
lower first ionization enthalpy ? (a) Cl or F ; (b) Cl or S ; (c) K or Ar ;
(d)Kr or Xe
...
Why do elements in the same group have generally similar
properties?
8
...
9
...
10
...
Give the
general electronic configuration of each block
...
To which block does the element with configuration 3d104s2 belongs
12
...
E
...
Out of fluorine and chlorine, which has greater electron gain
enthalpy?
14
...
What property did Mendeleev use to classify elements in his periodic
table?
16
...
Explain briefly the following
1
...
Which of the following pairs of elements would have higher electron
gain enthalpy? (a) N or O ; (b) F or Cl
...
3
...
Explain the reason for this arrangement ?
4
...
5
...
Name the different transition series
...
Which element of the following pairs have smaller ionization
enthalpy? (a) Ca or Be ; (b) Ca or K ; (c) Cl or I
...
7
...
What do you mean by the term electron gain enthalpy? How does
electron gain enthalpy change along a period and in a group?
9
...
10
...
What are the differences between normal and transition elements?
12
...
13
...
14
...
Give the general variation of electron gain enthalpies in the periodic
table
...
Define the term ionic radius
...
17
...
What is meant by electronegativity? On what factors does it depend?
19
...
SUMMARY
In this Chapter, Historical Survey and review of Periodic Classifications
are presented
...
Modern Periodic
table is explained in detail
...
Latest IUPAC
nomenclature of elements is also explained for elements having atomic
number greater than 100 is explained
...
Their trends along the
period and down the group are explained with suitable examples
...
REFERENCE
Concise
...
D
...
108
s - BLOCK ELEMENTS
1
H
1
2
2
Li
Be
d
3
Na
Mg
3
4
K
Ca
5
Rb
Sr
6
Cs
Ba
7
Fr
Ra
ns 1
ns 2
ns 1-2
1
A lkali m etals
2
A lkaline earth m etals
109
5
...
• Understand the nature and application of different isotopes of
hydrogen
...
• Gain knowledge about the application of heavy water
...
• Understand the special feature of liquid hydrogen used as a fuel hydrogen economy
...
• Know about the basic nature of oxides and hydroxides
...
• Recognise the properties and understands the uses of lithium and
sodium
...
It has the simplest
electronic configuration 1s1
...
Isotopes:- Atoms of the same element having same atomic number but
different mass number are called isotopes
...
Table 5
...
No
Name
1
...
Deuterium
or heavy
hydrogen
3
...
984
2
1H
1
2
1
1
0
...
Protium or ordinary hydrogen: It is the common form of hydrogen
...
It
constitutes 99
...
Its mass number
is one
...
Deuterium or heavy hydrogen: 1H2 or 1D2
...
The proportion present in naturally occurring hydrogen is in
the approximate ratio: D: H~ 1:6000
...
However only a solitary electron is revolving around the nucleus
...
3
...
Unlike deuterium, it is radioactive, with a half-life of ~ 12
...
It's
nucleus consists of one proton and two neutrons
...
Methods of Preparation of deuterium
1
...
The lighter hydrogen diffuses more quickly than deuterium
through a porous partition under reduced pressure
...
The process of diffusion has been carried out in various diffusion
chambers called Hertz diffusion units
...
When the mixture is led into the diffusion units under reduced pressure
111
by the help of mercury diffusion pumps, the heavier deuterium diffuses less
readily while lighter hydrogen diffuses at faster rates
...
The efficiency of this process could be increased by
increasing the number of diffusion units
...
By fractional distillation of liquid hydrogen: By fractional
distillation of liquid hydrogen, it is possible to result in enrichment of the
last fraction in deuterium because deuterium boils at 23
...
2K
...
By electrolysis of heavy water: As water contains about one part
of heavy water in 6000 parts, at first, the concentration of heavy water is
increased by fractional electrolysis of water containing an alkali between
nickel electrodes
...
From heavy water, it is possible to get deuterium by decomposing it
with sodium, red hot iron or tungsten or by its electrolysis containing
sodium carbonate
...
Deuterium obtained can be further obtained in purified state by the
diffusion process
...
The
values of boiling point, melting point, vapour pressure, dissociation energy
and latent heat of fusion are found to be lower for protium than deuterium
...
112
1
...
2 D2 + O2
2D2O
...
Reaction with halogens: Like hydrogen, it combines with halogens
under suitable conditions to form their deuterides
...
Reaction with nitrogen: Like hydrogen, it combines with nitrogen
in the presence of a catalyst to form nitrogen deuteride which are also
known as heavy ammonia or deutero ammonia
...
Reaction with metals: Like hydrogen, it reacts with alkali metals at
high temperatures (633K) to form deuterides
2 Na + D2
2 NaD
5
...
For example, a mixture of deuterium and ethylene
when passed over heated nickel, gives Ethylene deuteride which is
saturated hydrocarbon like ethane
...
Exchange reactions: Deuterium and hydrogen atoms undergo
ready exchange with H2, NH3, H2O and CH4 deuterium slowly exchanges
their hydrogens partially or completely at high temperatures
...
It is used as tracers in the study of mechanism of chemical
reactions
...
High speed deuterons are used in artificial radioactivity
...
Its oxide known as heavy water (D2O) which is employed as
moderator in nuclear reactor to slow down the speed of fast moving
neutrons
...
Its traces are found in
nature due to nuclear reactions induced by cosmic rays
...
4 years
...
3
1T
3
o
2He + -1e
Uses
(i) It is used as a radioactive tracer in chemical research
...
5
...
When
two hydrogen atoms combine, they form molecular hydrogen
...
Hydrogen molecule
in which both the protons in the nuclei of both H-atoms are known to spin
in same direction is termed as ortho hydrogen
...
e
P
e
+
P
e
+
P
e
+
P
+
Parahydrogen
O rthohydrogen
At room temperature ordinary hydrogen consists of about 75% ortho
and 25% para form
...
At 25K
...
The change in the proportion of the two forms of hydrogen
requires a catalyst such as platinum or atomic hydrogen or silent electric
discharge
...
The
charcoal absorbs almost pure para hydrogen
...
Conversion of para into ortho hydrogen
Ortho hydrogen is more stable than para hydrogen
...
i
...
iii
...
v
...
By mixing with paramagnetic molecules like O2, NO, NO2
...
Properties: Ortho and para hydrogen are similar in chemical properties
but differ in some of the physical properties
...
83K while that of ordinary
hydrogen is 13
...
115
(ii) Boiling point of para hydrogen 20
...
39K
...
(iv) The magnetic moment of para hydrogen is zero since the spins
neutralise each other while in the case of ortho , it is twice than that of a
proton
...
5
...
The oxide of heavy hydrogen
(deuterium) is called heavy water
...
By experimental data he showed that `ordinary water', H2O contains
small proportion of heavy water, D2O (about 1 part in 5000)
...
Generally it is prepared by exhaustive electolysis
...
Taylor, Eyring and
First in 1933 formulated the electrolysis of water in seven stages using N/2NaOH solution and strip nickel electrodes
...
The cell itself serves as the cathode while the anode consists of a cylindrical
sheet of nickel with a number of holes punched in it
...
The gases
obtained from each stage are separately burnt and the water thus formed is
returned to the previous stage
...
The process usually consists of five stages
...
This method utilises the small difference in
boiling points of protium oxide (H2O) and deuterium oxide (D2O)
...
998
0oC
100oC
1
...
00
72
...
017
3
...
42oC
1
...
6oC)
1
...
8 dynes/cm
82
...
09 millipoises
80
...
6 millipoises
The solubilities of substances in heavy water also differ from those in
ordinary water
...
Physical Properties
Heavy water is a colourless, odourless and tasteless mobile liquid
...
Chemical Properties
The difference in chemical behaviour between H2O and D2O is very
slight
...
Important reactions of heavy water
1
...
2 Na + 2 D2O
2 NaOD + D2
Sodium deuteroxide
Ca + 2 D2O
Ca (OD)2 + D2
Calcium deuteroxide
2
...
Na2O + D2O → 2 NaOD
CaO + D2O → Ca(OD)2
3
...
SO3 + D2O
→ D2 SO4
Deutero sulphuric acid
P2O5 + 3D2O → 2D3 PO4
Deuterophosphoric acid
4
...
2D2O
2D2 + O2
5
...
Cu SO4
...
10D2O, NiCl2
...
Exchange reactions
When compounds containing hydrogen are treated with D2O, hydrogen
undergoes an exchange for deuterium
...
The tobacco seeds do not grow in heavy water
...
Certain moulds have been found to develop better in heavy water
...
As a neutron moderator, in nuclear reactors
...
It is used as a tracer compound in the study of reactions occurring in
living organisms
...
It is used for the preparation of deuterium
...
3 Hydrogen peroxide
Hydrogen peroxide was first prepared by L
...
Thenard, in 1813 by the
action of dilute acid on barium peroxide
...
Laboratory preparation of hydrogen peroxide
1
...
Calculated quantity of Na2O2 is added in small proportions to a 20% ice
cold solution of sulphuric acid
...
2
...
H2O2 is manufactured by the electrolysis of 50% sulphuric acid
followed by vacuum distillation
...
Reactions
H2SO4
2HSO4H2S2O8 + H2O
H2SO5 + H2O
2H+ + 2e-
H+ + HSO4H2S2O8 + 2e- (At anode)
H2SO4 + H2SO5
H2SO4 + H2O2
H2 (At cathode)
Concentration of hydrogenperoxide solution
119
The impurities like organic material or metallic ions, may catalyse its
explosive decomposition
...
ii) By distillation under reduced pressure at temperatures below 330K,
the concentration up to 90% solution is used till crystallisation formed
...
T
...
Properties
Physical
H2O2 is a colourless, odourless, syrupy liquid in the anhydrous state
...
Chemical
Pure H2O2 is unstable and decomposes on standing
...
2H2O2
2H2O + O2
Oxidizing Properties
H2O2 is a powerful oxidizing agent
...
H2O2 + 2H+ + 2e-
2 H2O
(In acidic solution)
H2O2- + 2e-
2OH(In alkaline solution)
i) It oxidises PbS to PbSO4
PbS+ 4H2O2
PbSO4 +4H2O
ii) It oxidizes ferrous salts into ferric salts
...
Delicate materials like silk, wool,
hair which will be destroyed by chlorine, are bleached with H2O2
...
Moist
silver oxide, acidified KMnO4, ozone, chlorine and alkaline solutions of
ferricyanides are reduced
...
ii) It destroys the colour of some organic compounds and is used in
bleaching delicate things like hair, wool, silk ivory and feathers
...
iv) It is also used as a propellant in rockets
...
4 Liquid hydrogen as a fuel
The hydrogen atom has become a model for the structure of atom
...
Hydrogen is normally a colourless, odourless gas composed of
H2 molecules
...
But the future holds an even greater role for hydrogen
as a fuel
...
On burning, it
produces more heat per gram than any other fuel
...
When
hydrogen burns in air, the product is simply water
...
The burning of fossil fuels is a source of environmental pollutants
...
Controlling carbondioxide emissions into the atmosphere is a difficult
121
challenge, but the answer might lie in the conversion to a hydrogen
economy, hydrogen would become a major energy barrier
...
At present, in USA they
use car using a modified piston engine and has a hydrogen storage unit in
the tank
...
Hydrogen in not a primary energy source
...
1) It is produced by heating propane and steam at high temperature
and pressure in presence of the catalyst nickel
...
The CO2 is removed
by dissolving it in a basic aqueous solution
...
For example, electricity from solar photovoltic
collectors can be used as a source of energy to decompose water by
electrolysis
...
5
...
Elements
lithium, sodium, potassium, rubiduim, caesium and francium constitute
alkali metals
...
Ashes of plants are composed mainly of sodium and
potassium carbonates
...
The alkali metals are shiny white and soft
...
They can be readily cut with a knife
...
They are extremely reactive metals and form strong alkaline oxides
122
and hydroxides
...
The last metal of this group, francium is radioactive
...
Since the alkali metals are extremely reactive they occur only as
compounds in nature
...
All the alkali metals exhibit an oxidation state of +1
...
7
...
The
colours given by Li, Na and K are crimson red, yellow, lilac respectively
...
Table 5
...
Density: In general, these elements have high density due to the
close packing of atoms in their metallic crystals
...
Density of the elements increases
on moving down the group due to the increase in the mass of the atoms
with increasing atomic number
...
2
...
Hence there is an increase in atomic and ionic radii in
the same order
...
Melting and boiling points : All alkali metals have low melting and
boiling point due to the weak bonding in the crystal lattice
...
With the increase in the size of the metal
atoms, the repulsion of the non-bonding electron gets increased and
therefore melting and boiling points decreases on moving down the group
from Li to Cs
...
Ionization energy : The first ionization energies of alkali metals are
relatively low and decreases on moving down from Li to Cs
...
The second ionization energies of alkali metals are fairly high
...
5
...
Therefore they
M+ + 1eM
have strong electropositive character
...
The alkali metals are so highly electropositive that
they emit electrons when irradiated with light
...
Due to this property, Cs and K are used in
photoelectric cells
...
Oxidation state: All the alkali metals have only one electron in
their outermost valence shall
...
Thus, they are monovalent elements showing an oxidation
state of +1
...
Reducing properties : As alkali metals have low ionization energy,
they lose their valence electrons readily and thus bring about reduction
reaction
...
124
5
...
Lithium metal is obtained by the electrolysis of moisture free lithium
chloride in a crucible of thick porcelain using gas-coke splinter anode and
iron wire cathode
...
Lithium is also obtained by the electrolysis of a concentrated solution of
lithium chloride in pyridine or acetone
...
It's vapours impart calamine red colour to the flame
...
It gives alloys with number of
metals and forms amalgam
...
When heated in air above 450K, it burns to give lithium
monoxide and lithium nitride
4 Li + O2
2 Li2O
6 Li + N2
2 Li3N
2) It decomposes cold water forming lithium hydroxide and hydrogen
2 Li + 2 H2O
2 LiOH + H2
3) Lithium is a strongly electropositive metal and displaces hydrogen from
acid with the formation of corresponding lithium salts
...
With nitric acid, the action is
violent and metal melts and catches fire
...
2) As a deoxidizer in the preparation of copper and nickel
...
125
4) LiAlH4 is used as an reducing agent
...
Extraction of Sodium
Down's process : It is now manufactured by electrolysis of fused
sodium chloride
...
The anode is surrounded by a ring
shaped iron cathode enclosed in a wire gauze shell which also acts as a
partition and separates the two electrodes
...
Sodium is liberated at the cathode and remains in the wiregauze shell
...
2 NaCl
2Na + Cl2
126
Physical properties
1) It is a silvery white metal when freshly cut but is rapidly tarnished
in air
...
2) It is a soft metal
...
4) It dissolves in liquid ammonia forming an intense blue solution
...
2H2O
2CO2
4NaOH
Na2CO3 + 2H2O
2 Na2O
4Na + O2
When heated in air, it burns violently to form the monoxide and the
peroxide
...
2 Na + 2 H2O
2 NaOH + H2
3) Action of ammonia: Sodium gives sodamide with ammonia
liberating hydrogen
...
Sodium dissolved in liquid ammonia is used as a reducing agent in
organic chemistry
...
5) Reducing action: Reduces many compounds when heated with
them in the absence of air
Al2O3 + 6 Na
SiO2 + 4Na
2 Al + 3 Na2O
Si + 2 Na2O
...
4 Na + 3 CO2
2 Na2CO3 + C
...
Uses
1) For the preparation of sodium peroxide, sodamide and sodium
cyanide, tetraethyl lead etc
...
3) As a deoxidizing agent in the preparation of light alloys and some
rare earth metals from their oxides
...
5) As a reagent in organic chemistry
...
Choose the best answer
1
...
Deuterium nucleus consists of
(a) 2 protons only
(b) one neutron
(c) one proton and one neutron(d) 2 protons and one neutron
3
...
Tritium is prepared by bombarding lithium with
(a) deutrons
(b) mesons (c) slow neutrons (d) all helium nucleus
5
...
D2O reacts with P2O5 and gives
(b) D2PO4
(c) D3PO3
(d) D3PO4
(a) DPO4
7
...
H2O2 is a powerful
agent
(a) dehydrating
(b) oxidising (c) reducing (d) desulphurising
is used as a propellant in nucleus
9
...
The oxidation state of alkali metals is
(a) +2
(b) 0
(c) +1
(d) +3
colour
11
...
On moving down the group, density of the alkali metals
(a) increases
(b) decreases
(c) increases and then decreases (d) decreases and then increases
13
...
Fill in the blanks
...
The first element in the periodic table is
is the common formd of hydrogen
...
...
The half-life of tritium is
...
Deuterium reacts with ammonia to form
...
The rare isotope of hydrogen is
is employed in nuclear reactor to slow down the speed
6
...
...
The magnetic moment of para hydrogen is
...
Deuterium with salt and other compounds forms
...
Hydrogen peroxide was first prepared by __________ in
...
Pure H2O2 is
...
The Arabic word `Alquili' means
...
The electronic configuration of potassium is
melting and boiling points
...
All alkali metals have
...
On moving down the group of alkali metals, ionization energy
is the lightest of all solid elements
...
C
...
2
...
4
...
What are isotopes? Mention the isotopes of hydrogen
...
How does deuterium react with nitrogen?
How does deuterium react with metals?
Mention the uses of deuterium
...
How is tritium prepared?
7
...
How does heavy water react with metals?
9
...
How is hydrogen peroxide solution concentrated?
11
...
12
...
13
...
Why alkali metals have strong electropositive character?
D
...
2
...
4
...
6
...
8
...
How is deuterium obtained by diffusion process?
Write about the exchange reactions of deuterium
...
Differentiate between ortho and para hydrogen
...
Compare water and heavy water
...
Explain how liquid hydrogen can be used as a fuel
...
This
element heated in air gives compound A
...
With ammonia gives compound C, which is used as a
reducing agent in organic chemistry
...
Solution
(i) As per the position in the periodic table this element occupying
group number 1 and period number 3 is sodium
...
The compound A is sodium peroxide
...
The compound C is sodamide
...
An isotope of hydrogen reacts with oxygen to give compound (A),
which is used as a moderator in nuclear reactor
...
It reacts with ethylene to give compound
B, which is a saturated hydrocarbon
...
A is
radioactive
...
An isotope of hydrogen is prepared by bombarding beryllium with
deuterons
...
Identify the isotope and the element A
...
A deuterium compound (A) which is used as a moderator in nuclear
reactor reacts with Ca to form compound B
...
Upon electrolysis compound A gives deuterium molecule
...
4
...
This
element burns with air and forms compound A
...
Identify the
elements, A, B and C
...
It exists in 3
isotopes
...
The preparation properties of
deuterium are dealt in detail
...
It can be converted from one
to another form
...
It reacts with metals, metallic oxides, acid
anhydrides etc
...
131
In 1813, L
...
Thenard prepared hydrogen peroxide by the action of
dilute acid on barium peroxide
...
Pure
H2O2 is unstable
...
The use of liquid hydrogen as a fuel is explained in this chapter
...
There is mostly regular
gradation in properties like density, atomic volume, melting and boiling
point, ionization energy etc
...
The extraction of lithium and sodium and its properties are explained in
detail
...
General Chemistry - John Russell
McGraw Hill International Editions 3rd Edition
...
Inorganic Chemistry, P
...
Soni
...
GROUP 2 s - BLOCK ELEMENTS
OBJECTIVES
•
•
•
•
•
Understands the general characteristics of alkaline earth metals
Know the comparison of alkali and alkaline earth metals
...
Recognise the different compounds of alkaline earth metals
...
6
...
These elements are also a known as "Alkaline Earth Metals"
...
Radium corresponds to all the alkaline earth metals in its chemical
properties but being radioactive, it is studied along with other radioactive
elements
...
Electronic configuration
Element
At
No
...
Thus, the outer electronic configuration of each
element is ns2 where n is the number of the valence shell
...
Hence these elements are all bivalent and tend to form ionic
salts
...
Due to their alike
electronic structure, these elements resemble closely in physical and
chemical properties
...
These elements have been sufficiently soft yet less than the alkalimetals
as metallic bonding in these elements has been stronger than in first group
alkali elements
...
Magnesium and calcium are
abundant and among the eight most common elements in the earth's curst
...
Metallic properties
The alkaline earth metals are harder than the alkali metals
...
They show good metallic lustre
and high electrical as well as thermal conductivity because the two selectrons can easily move through the crystal lattice
...
They possess low melting and
boiling points
...
Atomic radius
The atoms of these elements are somewhat smaller than the atoms of
the corresponding alkali metals in the same period
...
Due to the smaller atomic radius, the elements, are harder, have
higher melting points and higher densities than the elements of group 1
...
Ionic radius
The ions are also large but smaller than those of the elements in group
1
...
The ionic radius is seen to increase on moving
down the group 2
...
Ionisation Energy
As the alkaline earth metals are having smaller size and greater nuclear
charge than the alkali metals, the electrons are more tightly held and hence
the first ionisation energy would be greater than that of the alkali metal
...
It is interesting to observe that although the IE2 of the alkaline earth
metals is much higher than the IE1 they are able to form, M2+ ions
...
As the atomic size gets increased from Be to Ba,
the values of IE1 and IE2 of these elements would decrease on going down
the group, ie, Be to Ba
...
It has the least tendency to form Be2+ ion
...
135
The total energy required to produce gaseous divalent ion for second
group elements is over four times greater than the amount needed to ionise
alkali metals
...
Oxidation states
Because of the presence of two s-electrons in the outermost orbital,
being high heat of hydration of the dipositive ions and comparatively low
value of IE2, the alkaline earth metals have been bivalent
...
Flame colouration
These elements and their compounds impart characteristic colours to
flame
...
The reason for imparting the colour to flame is that when elements or
their compounds are put into flame, the electrons get energy and excite to
higher energy levels
...
Beryllium and magnesium atoms are smaller and their electrons being
strongly bound to the nucleus are not excited to higher energy levels
...
Diagonal relationship between Beryllium and Aluminium
In case of beryllium, a member of second period of the periodic table,
which resembles more with Aluminium group (13 group) than the member
of its own group (2nd)
...
These two factors tend to increase the polarising power of Be2+ tends to
form ions to such extent that it is significantly equal to the polarising power
of Al3+ ions
...
6
...
The British chemist
Humphry Davy discovered the pure element magnesium in 1808
...
Important Ores
Magnesium does not occur in the native state
...
Magnesite, MgCO3
Epsomsalt, MgSO4, 7H2O
Dolomite, MgCO3, CaCO3
Carnallite MgCl2 KCl
...
The oceans are the best sources for
magnesium
...
Metallurgy
Magnesium is prepared on a large scale by the electrolysis of either
fused magnesium chloride or magnesia
...
Electrolysis of fused magnesium chloride
The purified carnallite ore is the principal source for this process
...
The alkali chloride prevents hydrolysis of magnesium chloride
and increases the conductivity of the fused mass
...
The temperature of the elctrolyte bath is maintained at 970K
...
Molten magnesium being lighter than the electrolyte, rises to the
surface and is periodically removed with perforated ladle
...
The metal thus obtained is 99
...
It may be
further purified by remelting with a flux of anhydrous magnesium chloride
and sodium chloride
...
At
slightly below its melting point, it is malleable and ductile and can be
drawn into wire or rolled into ribbon in which form it is generally sold
...
Chemical Properties
1
...
2
...
2Mg + O2 → 2Mg O
3Mg + N2 → Mg3N2
3
...
Action of Water
When heated with steam it burns brilliantly producing magnesium
oxide and hydrogen
...
Action of Acids
Dilute HCl or H2SO4 gives hydrogen with magnesium
...
With
concentrated HNO3, it gives ammonium nitrate
...
Displacement of Metals
It is a strongly electropositive metal and hence Mg displaces nearly all
the metals from the solutions of their salts eg
...
Reducing Action
Mg has great affinity for oxygen and it liberates sodium, potassium,
boron and silicon from their oxides at high temperatures
...
In flashlight photography, pyrotechnics and in fireworks
...
As a reducing agent in the preparation of boron and silicon and
deoxidiser in metallurgy
...
3 Compounds of alkaline earth metals
Magnesium sulphate, epsom slat, MgSO4
...
MgO + H2SO4 → MgSO4 + H2O
Uses
1) As a purgative
2) In dyeing and tanning processes and in dressing cotton goods
...
139
Calcium oxide, CaO, quicklime
It is prepared by burning limestone in specially designed kilns
...
Lime is a white porous solid
2
...
The
fine powder obtained is known as slaked lime and consists of calcium
hydroxide Ca(OH)2
...
CaO + H2O → Ca(OH)2
The paste of lime in water is called milk of lime whereas the filtered
and clear solution is known as lime water
...
With chlorine it gives bleaching powder CaOCl2
...
With carbondioxide, it forms calcium carbonate while with
sulphurdioxide, calcium sulphite is obtained
...
Moist hydrochloric acid gas reacts with it to give calcium chloride but
there is no action with the dry gas
...
3
...
For the manufacture of calcium chloride, cement, mortar and glass
...
As milk of lime, used in refining sugar and white washing
...
Calcium sulphate, CaSO4
It occurs as Anhydrite, CaSO4 and Gypsum CaSO4
...
It may be
prepared by adding dilute sulphuric acid to the solution of a calcium salt
...
For preparing plasters
2
...
The substance is known as plaster of paris because
the large deposits of Gypsum used for the manufacture of plaster are at
Montmeite (Paris)
...
A slight expansion
occurs during the setting so that it will take sharp impression of a mould
...
The final product of setting is gypsum
...
½H2O
setting step
hardening
CasO4
...
2 H2O
Step
The setting step may be catalysed by NaCl while it is retarded by borax
or alum
...
In surgery for plastering the fractured bones
...
In making moulds for statues, in dentistry etc
...
In making false ceilings
...
Choose the best Answer
1
...
(a) Sodium
(b) Calcium (c) Lithium
(d) Potassium
2
...
Among alkaline earth metals
ionization energy
...
The colour given by barium in flame is
(a) Brick red (b) Apple Green (c) Red
(d) Blue
5
...
Quick lime is
(a) Calcium oxide
(b) Calcium hydroxide
(c) Calcium nitrate (d) Calcium sulphate
7
...
H2O
(b) CaOCl2
...
2H2O
(d) CaSO4
...
Plaster of paris is
(a) CaSO4
...
2H2O
9
...
The element used in pyrotechnics is
(a) Magnesium
(b) Barium
(c) Calcium (d) Beryllium
B
...
The general electronic configuration of alkaline earth metals is
________
...
The ionic radius
on moving down the group 2
...
In flame, calcium gives__________ colour
...
Beryllium resembles more with an element in 13th group ________
...
Magnesium comes from the name of the mineral __________
...
__________ is present chlorophyll
...
Magnesium is prepared by the electrolysis of fused __________
...
8
...
The formula of epsom salt is __________
...
Epsom salt is used as _________
...
Match the following
1
...
3
...
5
...
2H2O
Mg Cl2
...
6H2O
MgCO3
MgCO3
...
7H2O
Problem
An element occupies group number 2 and period number 3
...
It is a
strong electropositive metal so it displaces Ag from AgNO3 solution
...
Identify the element,
compound A, B and C
...
Write in one or two sentence
1
...
Why there is increase in the ionisation potential for forming M3+ ion for
group 2 metals?
3
...
Why a precipitate of Mg(OH)2 is not formed when aqueous ammonia,
NH4OH is added to a solution of MgCl2?
5
...
6
...
Why group 2 elements are harder than alkali metals?
8
...
Why?
9
...
The basic strength of the oxides of group 2 elements increases from Be
to Ba
...
Explain briefly on the following
1
...
In what respects Be and Mg differ from all the other metals of group 2
...
How can you explain the anomalous behaviour of beryllium
...
How does magnesium occur in nature? How is the metal extracted from
its Ore?
5
...
a
...
These are good conductors of heat and electricity
...
Why the first ionization energy of alkaline earth metals higher than that
of Ist group
...
Mention the uses of plaster of Paris
...
How is plaster of paris prepared?
9
...
Mention the uses of Magnesium?
SUMMARY
The second group of periodic table is known as alkaline earth metals
...
The physical properties and chemical
of these elements are explained
...
Some compounds of alkaline earth metals such as
Epsom salt, calcium sulphate, quick lime, gypsum and plaster of paris are
dealt
...
General Chemistry - John Russell
McGraw Hill International Editions 3rd Edition
...
University General Chemistry
An Introduction to Chemical Science edited by CNR Rao
...
3
...
4
...
L
...
144
p - BLOCK ELEMENTS
18
ns 2 np1-5
17
1
13
14
15
16
d
B
C
N
O
F
2
12
Al
Si
P
S
Cl
3
Ga
Ge
As
Se
Br
4
In
Sn
Sb
Te
I
5
Tl
Pb
Bi
Po
At
6
7
ns 2np 1
ns2np2
ns2np3
ns 2np4
13
Boron group
14
Carbon group
15
Nitrogen group
16
Oxygen group
145
ns 2np5
7
...
* Know the important ores of boron
...
* Understand the preparation, properties and uses of boron
compounds
...
* Understand the structure of graphite and diamond and the
difference between them
...
* Learn about fixation of nitrogen
...
* Recognise the uses of nitrogen and its compounds
...
* Realise the importance of ozone to life
...
1 General Characteristics
The elements belonging to the group 13 to 18 of the periodic table, in
which p-orbitals are progressively filled are collectively known as p-block
elements
...
These are progressively filled by the addition of
one electron as we move from group 13 (ns2np1) to group 17 (ns2np5)
...
p-block elements show a variety of oxidation state both positive and
negative
...
This is known as `inert pair effect'
...
A full
explanation involves the decreasing strength of the M-X bond going down
the group (for covalent compounds) or the decreasing lattice energies of
compounds containing the M4+ ion (for ionic compounds)
...
MX2 + X2 →MX4
The existence of a positive oxidation state corresponding to the group
number and of another state two units lower is an illustration of the inert
pair effect, the term referring to the valence `s' electrons, used in bonding in
the higher oxidation state but not in the lower
...
The stability of such compounds with the +3 oxidation state is, however,
lower than those with the +1 oxidation state in the case of heavier members
of this group
...
This is because, the s electrons in the ns sub-shell do not prefer to
form bonds
...
This property of stabilising the
lower oxidation state keeping the paired electron in the ns orbital is referred
to as the `inert pair effect'
...
Nature of oxides
Oxides of p-block elements may be basic (in case of metallic elements),
amphoteric (in case of metalloids) or acidic (in case of non-metals)
...
In all the groups, the acidic
character of the oxide decreases as we move down the group while it
increases in the same period from left to right
...
Basic character increases down the group
CO2
acidic
SiO2
less acidic
GeO2
amphoteric
SnO
basic
PbO
most basic
Acidic character increases across a period
SiO2 P4O10 SO2 Cl2O7
Al2O3
amphoteric acidic
most acidic
Nature of hydrides
Many of the p-block elements form hydrides
...
Thus in any group the stability of the hydride
decreases from top to bottom; its strength as an acid also increases in this
order
...
In group 15, nitrogen forms the stablest hydride of
all
...
Metallic halides show a gradation from an ionic character to covalent
character
...
For example,
SbCl2 is partially ionic whereas TeCl4 is covalent
...
Polarizability of a halide ion depends on its size
...
7
...
In the combined state, it
occurs mainly in the form of the salts of boric acid
...
2
...
10H2O
7
...
2 Extraction
On a large scale, boron is extracted from its minerals, borax Na2B4O7 or
colemanite Ca2B6O11
...
2Ca2B6O11 + 3Na2CO3 + H2O → 3Na2B4O7 + 3CaCO3 + Ca(OH)2
The insoluble calcium carbonate settles down and borax is crystallized
from the mother liquor
...
a) Preparation of boron trioxide:- Borax is treated with hot
concentrated hydrochloric acid, when the sparingly soluble boric acid
slowly separates out
...
The residual boron is broken up and boiled with concentrated HCl
to dissolve out magnesium oxide and excess of boric acid when a dark
brown powder of amorphous boron is obtained as a residue: It is washed
with water and dried
...
Pure boron is obtained in the crystalline form by passing a mixture of
boron tribromide vapours and hydrogen over electrically heated filament of
tungsten at 1470K
...
Physical properties
149
Boron exists in two allotropic forms amorphous and crystalline boron
...
Chemical properties
1) Action of air:- It is unaffected by air at ordinary temperature but when
heated in air to about 975K, it burns forming boron trioxide and a little
boron nitride, BN
4B + 3O2 → 2B2O3
2B + N2 → 2BN
2) With acids: - Amorphous boron dissolves in hot concentrated sulphuric
and in nitric acid to form boric acid
...
3) With caustic alkali:- It dissolves in fused caustic alkali and forms
boric acid
...
3CO2 + 4B → 2B2O3 + 3C
3SiO2 + 4B → 2B2O3 + 3Si
5) With metals:- It combines with metals (except Cu, Ag and Au) at high
temperature in the electric furnace to form borides
...
Boron carbide is probably the hardest substance known
...
2
...
Borax can be prepared
i) From colemanite:- It is boiled with concentrated solution of sodium
carbonate
...
On filtration and concentration, crystals of borax separate
...
4NaBO2 + CO2 → Na2CO3 + Na2B4O7
The residual sodium carbonate is used again for the treatment of a fresh
quantity of colemanite
...
Properties
1
...
It then decomposes to give sodium meta borate and boron (III)
oxide
...
10H2O
Na2B4O7
∆ 2NaBO2 + B2O3
→
When this mixture is fused with metallic oxide it forms characteristic
coloured beads
...
For example
CuO + B2O3 → Cu(BO2)2
...
Borax bead test
A pinch of borax is heated in a platinum loop, it melts to give a
colourless glassy bead
...
Characteristic coloured beads are formed
...
Due to the formation
of metallic metaborate, the characteristic colours are formed
...
Metallic
compounds
Copper
Iron
Manganese
Cobalt
Chromium
Nickel
Colour in oxidising
flame
Blue
Yellow
Pinkish violet
Blue
Green
Brown
Colour in
reducing flame
Red
Bottle green
Colourless
Blue
Green
Grey
7
...
These are p-block elements having the
configuration ns2np2
...
No
...
3
...
Different amorphous varieties of carbon are (i) Coal, (ii) Coke,
(iii) Charcoal, (iv) Bone black or animal charcoal, (v) lampblack,
(vi) carbon black, (viii) Gas carbon and (ix) petroleum coke
...
3
...
Each carbon atom is linked
with four neighbouring carbon atoms held at the corners of a regular
tetrahedron by covalent bonds
...
The crystal
of diamond is very hard and has high melting and boiling points
...
Structure 7
...
153
Structure of graphite
It consists of separate layers
...
There is no strong bonding between
different layers, which are, therefore, easily separable from each other
...
Whilst the bonds within
the layers are strong, those between the layers are not and so they slide over
each other easily This accounts for the softness and lubricating power of
graphite
...
4 : The structure of graphite
...
The first to be identified and the most symmetrical of
the family, with 60 atoms and 32 sides (20 hexagons and 12 pentagons),
was nick named `buckyball' and was then named buck minister fullerene,
because it resembles the geodesic domes developed by an American
inventor called R
...
The group of spherical carbon
molecules is called fullerenes
...
Fullerene
Amorphous form of carbon
Amorphous carbon is the most reactive form of carbon
...
This form has structural features of graphite, such as
sheets and layers
...
General properties
7
...
4
...
Thus metallic character increases on descending the
group since ionization energy decreases on descending the group
...
Carbon gives a vast number of hydrides (alkanes), silicon and
germanium (silanes and germanes) whereas stannane (SnH4) and plumbane
(PbH4) are the only hydrides of tin and lead are known
...
The difference is probably
due to the difference in electronegativity between C and Si resulting in
difference between C-H and Si-H linkages
...
Tetrachlorides are usually fuming
liquids at ordinary temperature
...
This
is because due to the absence of d-orbitals
...
Tetrahalides of rest of the elements undergo hydrolysis
...
Lead
and tin do not form trihalides
...
Chlorides
1
...
2
...
Only tin and lead
form chlorides in which their oxidation state is +2, the other chlorides
existing solely in the +4 state
...
It is also soluble
in organic solvents
...
Lead(II) chloride is also
a solid
...
The chlorides of the group 14
elements in their +4 oxidation state illustrate further the change in
character of the elements from non-metal to metal down the group and
giving a solution which conducts electricity, and melts at 501°C
...
3
...
Carbides
Compounds of carbon with less electronegative elements (eg
...
) are called carbides
...
156
i) Ionic or salt-like eg
...
WC and
iii) Covalent eg
...
All the three types of carbides are prepared by heating the element or its
oxide with carbon or a hydrocarbon to a high temperature
...
The oxides show a marked trend in structure from the molecules of
carbondioxide to giant structures intermediate between ionic and
covalent lower down the group
...
The +2 oxidation state is the more stable state in the case of leadoxide,
and lead (IV) oxide decomposes on heating giving lead(II) oxide, a
solid that melts at 886°C
...
3
...
The ease of formation of oxoanions (SiO32-, GeO32-etc
...
The oxides
of germanium, tin and lead are amphoteric, reacting to form simple salts
with acids
...
Carbon and its compounds play an enormous role in the global
economy, eg
...
2
...
3
...
7
...
This group is called nitrogen
group
...
All
157
these elements have five electrons in their outermost orbitals
...
These three
electrons are equally distributed in three p-orbitals as px1 py1 pz1 which
correspond to half-filled configuration
...
This is known as inert pair
effect
...
Nitrogen was discovered in 1772 by Daniel Rutherford, a Scottish
physician and chemist
...
It is also abundant in the combined state as saltpetre (KNO3),
sodium nitrate (chile saltpetre) and ammonium salts
...
Fixation of nitrogen
The nitrogen present in the atmosphere is free or elementary nitrogen
whereas nitrogen present in various nitrogenous compounds is called
combined or fixed nitrogen
...
Method employed for fixation or bringing atmospheric nitrogen into
combination:
Manufacture of ammonia (Haber's process) :
A mixture of nitrogen and hydrogen in the ratio 1:3 under pressure
(200-900 atm) is passed over a catalyst finely divided iron and
molybdenum as promoter, heated to about 770K
...
Nitric oxide combines with more of oxygen to give nitrogen
dioxide which when absorbed in water in the presence of excess of air,
gives nitric acid (Ostwald's process)
...
4NO2 + 2H2O + O2
→
158
Ammonia and nitric acid manufactured above may be converted into
ammonium salts and nitrates suitable as fertilizers
...
Nitrogen fixation in nature
Due to electrical disturbances atmospheric nitrogen and oxygen
combine to give nitric oxide which gets further oxidised to nitrogen
dioxide
...
Here it reacts with bases of
the soil to give nitrates
...
g
...
, convert nitrogen into nitrogenous
compounds which can be directly assimilated by the plant
...
The nitrogen passes from atmosphere to
plants and animals, converted into useful products like ammonia, nitric acid
etc
...
This is due to the fact that combined nitrogen is constantly
passing back to the atmosphere
...
A m m on ium S alts
A dded as m a nures
D eath and
d eca y exc retion
A m m on ium
com pound s
in soil
Sy
n
Li
gh
tn
nt
in
he
(F t
g
e r ic
t il i n i
z e tr a
rs te
) s
C oal
Slow ca rbo n ization
io
u tr it
al n
A IR
ic
ot
bi ia
m te r
Sy ac
B
N itrification
d
an
th y
ea e ca
d
en
D estructive
d istilla tio n
D
D
A n im
al
m ia
ic
fro on
em s m
n
C h u re a m
t io
a n t ic
ca
M the
if i
n
i tr
sy
C hile
N itre
etc
...
Liquid ammonia is used as solvent
...
Ammonia is used as a refrigerant in ice-plants
...
Ammonia is used in the manufacture of artificial silk, urea, manures,
washing soda etc
...
Nitrous oxide mixed with oxygen is used as anaesthetic for minor
operations in dentistry and surgery
...
Nitrous acid is used in the manufacture of azo-dyes
...
Nitric acid is used in the manufacture of fertilizers, explosives like
TNT, GTN, etc
...
Nitric acid is used in the purification of gold and silver
...
Nitric acid is used in pickling of stainless steel
...
Nitric acid is used in the manufacture of perfumes, artificial silk,
medicines etc
...
Liquid nitrogen is used as a refrigerant
...
4
...
It was called as `aqua
tortis' by alchemists
...
It was first prepared by Glauber
(1650)
...
Traces of nitric acid occur in air where it is formed by electric sparks
through the mixture of nitrogen and moist oxygen
...
Preparation
1
...
NaNO3 + H2SO4 → NaHSO4 + HNO3
160
Vapours of nitric acid are condensed to a brown liquid in a receiver
cooled under cold water
...
2
...
Nitric acid is manufactured by blowing air into an electric arc struck
between two water cooled copper electrodes and spread into a disc with
the help of a magnetic field at right angle
...
2
...
Platinum gauze
4 NH3
4NO + 6H2O
1155K
2NO + O2
2 NO2
4NO2 + 2H2O + O2
4 HNO3
Dilute nitric acid may be concentrated by distillation until a constant
boiling point mixture is obtained (98%)
...
Crystals of pure nitric
acid may be obtained by cooling 98% acid in a freezing mixture
...
It is a colourless fuming liquid when pure, but may be coloured yellow
by its dissociation products mainly nitrogen dioxide
...
It has extremely corrosive action on the skin and causes painful sores
...
Pure acid has a specific gravity of 1
...
It boils at 359K and freezes to a
white solid (m
...
231K)
...
5 Oxygen group - group 16
The elements oxygen, sulphur, selenium, tellurium and polonium
constitute 16th group of the periodic table
...
Collectively they are called the 'chalcogens' or ore -forming
elements
...
Oxygen is a very important element in inorganic chemistry, since it
reacts with almost all the other elements
...
It exists in the free form as dioxygen or molecular oxygen and
makes up 20
...
7
...
Myoglobin is a similar substance in muscle tissue, acting as a
reservoir for the storage of oxygen and as a transport of oxygen within
muscle cells
...
The sixth position is vacant in free
hemoglobin but is occupied by oxygen in oxyhaemoglobin
...
HbO2
Oxyhaemoglobin
Hb + O2
oxyhaemoglobin is formed in the lungs and carried to the cells, where it
gives up its oxygen
...
After reaching the lungs, due to
hydrolysis CO2 is released
...
The dioxygen (or)
molecular oxygen is prepared by the green plants
...
Oxygen makes up 46
...
162
Practically all the elements react with dioxygen either at room
temperature (or) on heating except Pt, Au, W and Noble gases
...
Dioxygen is also called as molecular oxygen
...
It is therefore essential for life
...
The complex formed between dioxygen and haemoglobin (the red
pigment in blood) is of vital importance
...
7
...
1 Nascent oxygen and molecular oxygen
Oxygen molecule is very stable
...
This reaction is endothermic
O2 →>2@û+ NFDO
However, when an electric discharge is passed through oxygen at a very
low pressure, it dissociates to the extent of about 20%
...
Its
line spectrum shows that it consists of the free atoms
...
O2
→22 û+ N-
Reactions
1
...
The rise of temperature of platinum wire
under standardised conditions is a measure of the concentration of the
atomic oxygen in the gas
...
Formation of ozone
Atomic oxygen combines with molecular oxygen to give ozone which
may be condensed by means of liquid air
O2 + [O]
O3
3
...
With nitric oxide, a characteristic greenish - white
luminescence is produced
...
7
...
2 Oxides
Generally all the elements react with dioxygen to form oxides
...
Oxides may be classified depending on
their structure (or) their chemical properties
...
They have
low melting and boiling points, though some B2O3 and SiO2 form infinite
"giant molecules" and have high melting points
...
Some
oxides dissolve in water and thus forming acids
...
ii) Basic oxides
Metallic oxides are generally basic
...
Some oxides dissolve in water and form alkaline
solution
...
Examples : Tl2O3, Bi2O3 and ThO2
...
CaO + 2HCl → CaCl2 + H2O
If a metal exists in more than one oxidation state and they form more
than one oxide
eg
...
ZnO + 2NaOH → Na2ZnO2 + H2O
Sodium zincate
ZnO + 2HCl → ZnCl2 + H2O
iv) Peroxides
These oxides contain more oxygen than would be expelled from the
oxidation number of M
...
The metal belonging to the group I and II (Na2O2, BaO2) contain O22- ion
...
Oxides such as PbO2 react with acids liberate Cl2
PbO2 + 4HCl → PbCl2 + 2H2O + Cl2
v) Compound oxides
Some oxides behave as if they are compounds of the two oxides
...
Ferrous-ferric oxide (Fe3O4)
...
They react with acids and forms a mixture of ferrous and ferric salts
...
vii) Dioxides
They also contain higher proportion of O2 than expected
...
Ex
...
7 Ozone
Ozone is an allotropic form of oxygen and its molecular formula is O3
...
The presence of ozone in
extremely small quantities has been observed in the atmosphere in places
near the seaside (or) big lakes
...
Ozone is
particularly important since there is a layer of ozone in the upper
atmosphere which absorbs harmful UV radiations from the sun and protect
the people and other living organisms on the earth
...
The
commonly used ozoniser is Siemen's ozoniser
(i) Siemen's ozoniser
It consists of two concentric metal tubes sealed together at one end
...
A
current of pure dry oxygen at low temperature is passed through annular
space between the two tubes and by the silent action of electric discharge,
the oxygen is partially converted into ozone
...
T IN FO IL
D ry O 2
-
+
Ind uction C oil
166
Properties
(i) Physical properties
It is a light blue gas which condense at 160
...
This liquid freezes at 23
...
Chemical properties
1) Decomposition : Pure ozone decomposes with an explosive violence
...
i) Lead sulphide is oxidised to lead sulphate
PbS + 4O3 → PbSO4 + 4O2
ii) Potassium manganate is oxidised to potassium permanganate
2K2MnO4 + H2O + O3 → 2KMnO4 + 2KOH + O2
3) Ozone reacts with peroxides and reduces it to oxides with the liberation
of oxygen
...
2) It is used for bleaching oils, ivory, flour, starch, etc
...
Ozone structure
0
...
8
8
12
nm
The ozone molecule consists of three oxygen atoms having a bent
structure
167
Each O atom contributes six valence electrons and so the total 3x6=18
electrons
...
Ozone layer
Ozone is produced in the upper atmosphere through absorption of a
SKRWRQK#RIXOWUDYLROHWOLJKWE\DQ22 molecule
...
The so-called ozone
shield is a shell about 30 km altitude which contains enough ozone to
absorb short wavelength UV radiation (less than 300 nm)
...
The absorption causes
dissociation of O3 to reform O2
...
In recent years, the shield is damaged mainly by supersonic aircraft and
168
chlorofluorocarbon products in the jet exhaust reduce ozone, and decreases
its concentration in the shield
...
CFC's are used as refrigerants and as propellants in some "aerosol sprays"
...
It is reported
that the holes caused in the ozone layer over the Antarctic and Arctic ocean
are due to the use of CFCs in aerosols and refrigerators
...
UV
CFC → Cl(g)
Cl(g) + O3(g)→ ClO(g) + O2(g)
ClO + O(g) → Cl(g) + O2(g)
O3(g) + O(g) → 2O2(g)
It is also seen that the oxides of nitrogen (from car exhausts) and the
halogen can damage the ozone layer
...
Questions
A
...
The oxides of non-metals are usually
a) ionic
b) coordinate c) covalent
d) none of the above
9
...
Fixation of nitrogen is a source for
a) Various oxygen compounds b) Various phosphorus compounds
c) Various nitrogen compounds d) Various sulphur compounds
11
...
a) Nitrous acid
b) Nitric acid c) Hyponitrous acid d) Pernitric acid
12
...
Anaesthetic used for minor operation dentistry
a) nitrous oxide
b) nitric oxide
c) nitrous oxide + oxygen d) nitrogen dioxide
14
...
a) graphite
b) diamond
c) fullerene
d) carbon black
B
...
The general electronic configuration of Boron group elements is
...
2
...
analysis
...
4
...
In diamond, every carbon atom is bonded with the other by
bond
...
6
...
7
...
8
...
9
...
10
...
11
...
Atomic oxygen combines with molecular oxygen to give
...
The ozoniser commonly used in the preparation of ozone are
_______
...
14
...
15
...
Match the following
a
...
Borax
a
...
Graphite b
...
ZnO
c
...
CFCs
d
...
Fertilizer
5
...
Fixation of nitrogen
b
...
Inert pair effect a
...
Oxyacid
b
...
Liquid nitrogen c
...
Ostwald process d
...
Molecular oxygen e
...
Refrigerant
c
...
Copper
a
...
Iron
b
...
Manganese
c
...
Cobalt
d
...
Chromium
e
...
Green
D
...
Mention the reasons for the stabilisation of lower oxidation state of
p-block element
...
Show the electron accepting property of boron trifluoride by giving an
example
...
Give an example of monovalent and trivalent element in group III
...
Why diamond is hard compared with graphite?
5
...
Boron does not form B3+ ion
...
Why NH3 has high boiling point than PH3?
8
...
Why?
9
...
Mention any 3 uses of ozone
...
What are CFC's? Mention its environmental action
...
What are compound oxides? Give an example
...
Mention the metal ions present in haemoglobin and myoglobin and
state its function
...
What happens when ozone reacts with
a) lead sulphide b) potassium manganate
E
...
Explain inert pair effect with suitable example
...
Give an account of nature of hydrides of 15th group elements
...
How is boron extracted from borax?
4
...
H2SO4 b) conc
...
How is borax prepared from colemanite?
6
...
Discuss the structural difference between diamond and graphite
...
Write a short note on fixation of nitrogen
...
How nitric acid is prepared by ostwald process
...
Why silicon carbide is used as an abrasive?
11
...
How ozone reacts with the following (a) PbS (b) KmnO4
Problem
An element occupies group no
...
(A) reacts with CuSO4 give blue beads (B)
...
Write the reaction
...
Cu(BO2)2
Attempt the following problem
...
BF3 reacts with LiH and forms a compound A
...
A reacts with ammonia at 390 K
and form C
...
2
...
In presence of excess of air and in the presence of platinum
it forms an oxyacid (B)
...
3
...
16 and period number 2
...
(A) also reacts
with lead sulphide and forms (B)
...
It reacts with H2O2 and forms (D)
...
4
...
14 and period number 2 exists in
different allotropic forms
...
Another form is the hardest substance (B)
...
Identify the element, (A) (B) and (C)
...
The lower oxidation states of these elements are stabilised by inert pair
effect
...
The element boron is extracted
from its ore borax and colemanite
...
Most
173
important of them is borax, which is used to identify the metallic radicals in
the qualitative analysis
...
Carbon exists in different
allotropic forms such as diamond, graphite, fullerenes and other amorphous
form
...
Group 15 is known as nitrogen group
...
It plays a vital role in fixation of nitrogen and the importance
can be studied by the nitrogen cycle
...
It is prepared by
Ostwald process
...
Group 16 is known as oxygen group
...
Dioxygen or molecular oxygen plays an important role in
functioning of haemoglobin and myoglobin
...
The
causes of ozone depletion must be considered seriously and steps should be
taken to stop the depletion
...
General Chemistry - John Russell
McGraw Hill International Editions 3rd Edition
...
University General Chemistry
An Introduction to Chemical Science edited by CNR Rao
...
3
...
4
...
L
...
174
PHYSICAL CHEMISTRY
8
...
Difference between crystalline and an amorphous materials
...
Study of Sodium Chloride and Cesium Chloride unit cells
...
Learn to identify the important planes in a cubic system in terms of
Miller indices
...
8
...
In
these solids the atoms or molecules are arranged in a very regular and
orderly fashion in a three dimensional pattern
...
The X-ray diffraction studies reveal that their ultimate particles (viz
...
This definite and
ordered arrangement of molecules, atoms or ions (as the case may be)
extends over a large distance
...
The outstanding characteristics of a crystalline solid are its sharp
melting point
...
g
...
Amorphous solids
There is another category of solids such as glass, rubber and plastics,
which possess properties of incompressibility and rigidity to a certain
extent but do not have definite geometrical forms
...
These solids lack well-defined faces and shapes
...
Most others are composed of large complicated molecules
...
Thus, amorphous solids do not melt at
specific temperatures
...
Amorphous solids are isotropic as they exhibit same physical
properties in all the directions
...
Crystalline
and amorphous solids differ from one another in the following respects
1
...
An amorphous solid, on the other hand, does not have any pattern
of arrangement of molecules or atoms and, therefore, does not have any
define geometrical shape
...
Thus unlike crystalline
solids, amorphous solids do not have a long range order
...
Melting points
As a solid is heated, it's molecular vibrations increase and ultimately
becomes so great that molecules break away from their fixed positions
...
The solid now changes into liquid state
...
A crystalline substance has a sharp melting point, i
...
, it changes
abruptly into liquid state
...
For example, if glass is heated gradually,
it softens and starts to flow without undergoing a definite and abrupt
176
change into liquid state
...
There is some justification for this view
because it is known form X-ray examination that amorphous substance
do not have well-ordered molecular or atomic arrangements
...
e
...
3
...
The properties such as electrical
conductivity thermal conductivity, mechanical strength and refractive
index are the same in all directions
...
Liquids and gases are also isotropic
...
e
...
For example, the velocity of light
passing through a crystal varies with the direction in which it is
measured
...
This phenomenon is known as double refraction
...
This can be shown on
reference to Fig
...
1 in which a simple two-dimensional arrangement of
only two different kinds of atoms is depicted
...
8
...
The reason is that while in the
first case, each row is made up of alternate type of atoms, in the second
case, each row is made up of one type of atoms only
...
Size and shape of crystals
Several naturally occurring solids have definite crystalline shapes,
which can be recognized easily
...
But when an individual particle is examined under a
microscope, it is also seen to have a definite crystalline shape
...
The size
of a crystal depends on the rate at which it is formed: the slower the rate
the bigger the crystal
...
Thus,
large transparent crystals of sodium chloride, silver chloride, lithium
chloride, etc
...
It is for this reason that crystals of
most of the minerals formed by geological processes are often very large
...
Faces: Crystals are bound by plane faces
...
Faces are of two types:
Like: A crystal having all faces alike e
...
Fluorspar
...
g
...
ii) Form: All the faces corresponding to a crystal are said to constitute a
form
...
178
iv) Interfacial Angle: The angle between the normals to the two
intersecting faces is called interfacial angle
...
, yet
the interfacial angles for any two corresponding faces of the crystals
remain invariably the same throughout
...
The measurement of interfacial angles in crystals is, therefore,
important in the study of crystals
...
8
...
The smallest structure of which the crystalline solid (or
crystal) is built by its repetition in three dimensions is called as unit cell
...
Therefore, a unit cell is the fundamental elementary pattern of a
crystalline solid
...
Characteristic parameters of unit cell
1
...
2
...
3
...
179
Crystallographic axes : OX, OY, OZ
Interfacial angles
: α, β, γ
Primitives (distances) : a, b, c
The unit cell is characterized by the distances a, b and c and angles α,
β & γ
...
Because a unit cell is representative of the
entire structure, the ratio of ions in the unit cell is the same as the ratio in
the overall structure
...
1
...
Triclinic,
3
...
Orthorhombic, 5
...
Hexagonal and
7
...
Packing arrangement variations exist in each of the classes, yet here
we will only explore the cubic system because it is the simplest
...
Each unit
cell is defined by one type of atom
...
(Ignore all other types
...
This is
where one atom occupies each of the eight corners of a cube
...
180
Body-centred cubic
The next unit cell is known as the body-centred cubic
...
This packing can fit more
atoms into less space than the simple cubic unit cell
...
In this form of crystal, there is an atom at each corner of the unit
cell
...
This crystal packing form has an even higher density than
the body-centred cubic unit cell
...
The lattice
position of the atom or ion determines the number of unit cells involved
in the share
...
Body: Not shared
Face: Shared by two unit cells
Edge: Shared by four unit cells
Corner: Shared by eight unit cells
...
A unit cell of this combined lattice is shown in figure
...
The
yellow spheres indicate chloride ions and red spheres represent sodium
ions
...
All electrovalent compounds show such lattices
...
Each chloride ion is surrounded by 6
sodium ions and similarly, each sodium ion is surrounded by 6 chloride
ions
...
Instead these particles are shared by other unit cells
...
The unit cell
of sodium chloride has 4 sodium ions and 4 chloride ions as shown
below;
No
...
of Chloride ions
= 8 (At corners) x (1/8) + 6 ( At face centre) x (1/2 )
= 8 x (1/8) + 6 x (1/2) =1+ 3 = 4
Thus, number of NaCl units per unit cell is 4
...
Representative crystals having the NaCl arrangements includes: LiH,
NaI, KCl, RbF, RbI, PbS etc
...
The body-centred cubic arrangement of atoms is
not a close packed structure
...
182
1
...
Each Cs+ ion is connected eight Cl- ions and each Cl- ion is
connected eight Cs+ ions i
...
, 8:8 coordination
...
The unit cell of cesium chloride has one Cs+ ion and one Cl- ion as
shown below
No
...
of Cs+ ion = 1 (At the body center) x 1
= 1x1=1
Thus number of CsCl units per unit cell is 1
...
8
...
The number and
inclination of these crystal intercept them at definite distances from the
origin or are parallel to some of the axes, i
...
, intercepting at infinity
...
183
For example consider plane LMN in the crystal shown in Fig
...
2
...
8
...
These
intercepts are in the ratio of 2a : 4b : 3c wherein 2, 4, 3 are simple
integral whole numbers
...
It may be borne in mind that the Weiss
indices are not always simple integral whole numbers as in this case
...
Weiss indices are, therefore, rather awkward in use and have
consequently been replaced by miller indices
...
The Miller indices for a particular family of planes are usually
written (h, k, l) where h, k and l are positive or negative integers or zero
...
Taking reciprocals of coefficients of a, b and c, we get the ratio 1/2, 1/4,
1/3
...
These numbers are called the Miller indices of the plane, and
the plane is designated as the (634) plane
...
184
Similarly the Miller’s indices for the plane which the Weiss notation
is given by ∞ a : 2b : c
...
e
...
Multiplying by 2 in order to
convert them into whole numbers, we get 0, 1, 2
...
The distances between parallel planes in a crystal are designated as
dhkl
...
Definition of Miller Indices in three dimensions
A pair of planes with Miller indices (213)
The Miller indices of a face of a crystal are inversely proportional to
the intercepts of that face on the various axes
...
E
...
1/2 x a, 1x b, 1/3 x c
...
Prepare a three-column table with the unit cell axes at the tops of the
columns
...
Enter in each column the intercept (expressed as a multiple of a, b or
c) of the plane with these axes
...
Invert all numbers
...
Clear fractions to obtain h, k and l
...
To determine the Miller
indices, one finds the intercepts on the three axis
...
Then the reciprocals are taken, ie
...
, 3, 6, 4 by
12
...
Let us look at the most common planes in a cube, shown below in
figure
...
The front crystal face intersects only one of the crystallographic axes(xaxes)
...
The side plane has
intercepts
186
x = ∞, y = 1, z = ∞ because the plane is parallel to the x- and z-axes,
forming the Miller indices gives (010)
...
The (110) plane intercepts x=1, y=1 and z= ∞ which is parallel to zaxis
...
The (111) plane
intercepts all the three axes x=1, y=1 and z=1
...
Solution : following the procedure given above, we prepare the tables as
follows:
187
(i) a
b
c
2
3
1 intercepts
½
1/3
1 reciprocals
3
2
6 clear fractions
Hence, the Miller indices are (326)
...
(iii) a
b
c
6
3
3 intercepts
1/6
1/3
1/3 reciprocals
1
2
2 clear fractions
Hence, the Miller indices are (122)
...
Note: The negative sign in the Miller indices is indicated by placing a
bar on the integer
...
Example 2: How do the spacings of the three planes (100), (110) and
(111) of cubic lattice vary?
Applying the formula
d hkl =
d (100) =
d (110) =
a
h 2 + k 2 + l2
a
12 + 0 + 0
a
1 +1 + 0
2
188
2
=a
=
a
2
d (111) =
a
12 + 12 + 12
=
a
3
Thus d(100) : d(110) : d(111) = 1: 1/√2: 1/√3
= 1: 0
...
577
Example 3: A metallic element exists as a cubic lattice
...
88Å
...
20 g cm-3
...
88Å)3 = 23
...
9 cm3
Number of unit cells in this volume
13
...
82 x 1023
-24
23
...
c
...
Hence n = 8 x (1/8) = 1
(ii) The b
...
c unit cell consists of 8 atoms at the 8 corners and one atom
at the centre
...
Thus the contribution of the 8 corners is 8 x (1/8) = 1 while that of the
body-centred atom is 1
...
There is
one atom each of the 6 faces, which is shared by 2 unit cells each
...
Example 5 : At room temperature, pollonium crystallizes in a primitive
cubic unit cell
...
36Å, calculate the theoretical density of
pollonium; its atomic mass is 209 g mol-1
...
Hence n = 8 x (1/8) = 1
...
36Å)3
nMm
From Eq
...
022 x 1023 mol-1) (3
...
15 g cm-3
Questions
A
...
The structure of sodium chloride crystal is:
(a) body centred cubic lattice
(b) face centred cubic lattice
(c) octahedral
(d) square planar
2
...
The 8:8 type of packing is present in:
(a) CsCl (b) KCl (c) NaCl (d) MgF2
4
...
An amorphous solid is :
(a) NaCl (b) CaF2 (c) glass (d) CsCl
6
...
In a body centred cubic cell, an atom at the body of centre is shared
by:
(a) 1 unit cell (b) 2 unit cells (c) 3 unit cells (d) 4 unit cells
190
8
...
In a face centred cubic cell, an atom at the face centre is shared by:
(a) 4 unit cell (b) 2 unit cells (c) 1 unit cells(d) 6 unit cells
Answers:
1) b 2) a 3) a 4) c 5) c 6) b 7) a 8)d 9) b
B
...
In NaCl ionic crystal each Na+ ion is surrounded by -------- Cl- ions
and each Cl- ion is surrounded by -------- Na+ ions
...
The coordination number of Cs+ in CsCl crystal is ----------3
...
4
...
5
...
A crystal may have a number of planes or axes of symmetry but it
possesses only one ----- of symmetry
...
Amorphous solids that exhibit same physical properties in all the
directions are called ---------
...
Crystalline solids that exhibit different physical properties in all
directions are called ---------
...
The number of atoms in a single unit cell of cubic close packed
sphere is --------10
...
11
...
Its miller indices will
be -----and the plane is designated as ---------
...
A plane is parallel to x & z axes and makes unit intercepts along
y-axis
...
Its Miller indices are --------
...
Answers :
(1) 6, 6
(2) 8 (3) Amorphous, supercooled (4) Centre
(5) simple cubic,bcc, fcc
(6) Centre
(7) isotropic
(8) Anisotropic (9) 4 (10) 1 (11) 2, 2, 2; (222) plane
(12) ∞, 1, ∞ ; 0, 1, 0 ; (010) plane
191
C
...
2
...
4
...
Write in one or two sentence :
What governs the packing of particles in crystals?
What is meant by ‘unit cell’ in crystallography?
How many types of cubic unit cell exits?
What are Miller Indices?
Mention the number of sodium and chloride ions in each unit cell of
NaCl
6
...
Explain briefly on the following :
1
...
Give the distinguishing features of crystalline solids and amorphous
solids
...
Explain the terms Isotropy and Anisotropy
...
What is the difference between body centred cubic and face centred
cubic?
5
...
6
...
Problems
1
...
How do the spacings of the three planes (100), (101) and (111) of
simple cubic lattice vary?
Ans: 1: 1/ √ 2 : 1/ √ 3
3
...
How do the spacings of the three planes (010), (110) and (111) of fcc
lattice vary?
Ans: 1/2 : 1/ 2√ 2 : 1/ √ 3
192
SUMMARY
Solids form an important part of the world around us, providing
materials with a definite shape and predictable properties
...
Amorphous solids have no long-range ordering in their structures
...
Lattice refers to the three dimensional array of particles in a
crystalline solid
...
A simple cubic unit cell has lattice points only at the eight corners of
a cube
...
A face-centred cubic unit cell has the same kind of particles (lattice
paints) at the eight corners of a cube and at the centre of each face
...
The miller indices of a face of a crystal are inversely proportional to
the intercepts of that face on the various axes
...
REFERENCES
1
...
V
...
2
...
Kittel, Introduction to Solid State Physics, Third edition, John
Wiley, 1966
...
A
...
Wells, Structural Inorganic Chemistry, Oxford University Press,
1962
...
Anthony R
...
193
9
...
To learn various gas laws and ideal gas equation
To learn different units of gas constant `R'
...
To analyse the deviation of ideal behaviour and to know Vanderwaal's
equation of state
...
To understand Joule - Thomson effect and the role of inversion
temperature
...
9
...
A
substance may be made to exist in any one of the three states by varying the
temperature or pressure or both
...
The energy of
motion known as kinetic energy is present in the gaseous molecules
...
A gaseous state can be described in terms of four parameters which are
known as measurable properties such as the volume, V; Pressure, P;
Temperature, T and Number of moles, n of the gas in the container
...
Due to their constant motion,
the molecules may not collide against one another very frequently, but can
strike against the walls of the containing vessel
...
Pressure is defined as force per unit area
...
The greater the number of molecules
striking per unit area of the walls in one second, the greater would be the
pressure exerted by the gas
...
Temperature effect
The kinetic energy of molecules is given by 1/2 mv2 where m is the
mass of the molecule and v is the velocity of its motion
...
Although the mass of the molecule
remains constant, its velocity increases
...
Therefore the molecules strike the wall of the containing vessel
more frequently
...
Therefore the pressure of the gas increases with rise in
temperature when the amount and its volume remain constant
...
This is considered from the postulates of kinetic theory of gases
...
Volume of gas is determined by its pressure,
temperature and number of moles at any instant
...
When `n' increases the number of molecules
colliding against the wall of container increases
...
When the amount of gas increases the volume occupied
by themselves also, increases
...
2 The gas laws
Boyle's law
Robert Boyle in 1662, studied the effect of change of pressure on the
volume of a given mass of gas at constant temperature
...
1
3
...
Thus if V1 is the volume occupied by a given mass of a gas at pressure
P1 and V2 is the volume when pressure changes to P2, then as the
temperature remains constant, according to Boyle's law
P1 V1 = P2 V2
= Constant
Charle's Law
The variation in the volume of a gas with temperature at constant
pressure is given by charle's law
...
V
...
7
(or)
P
__ = Constant
T
where T is temperature in kelvin
...
By combining these two laws, an equation of state of an ideal gas
can be derived
...
1
__
V
From Charle's law
3
...
T
__
(or)
39
...
Generally, the ideal gas equation is written as
PV = n RT
where `n' is the number of moles of the gas
...
of moles = ____________________ = ___ = mol
PV
Molecular mass of the gas
in gmol-1
m
___ RT
=
M
M
m = mass of the gas
...
T
...
013 x 105 Nm-2 (1 atm)
...
9
...
a
...
T
...
4 litre and thus
198
At STP
P = 1 atm
V=
R = PV/T (for 1 mole)
22
...
4)/273
Fig
...
1 Total pressure equals the sum of partial pressures of
T = 273 K
R = 0
...
0821 dm3
...
In C
...
S
...
6 x 980 dyne cm-2
= 1
...
013 x 106 x 22400
_____ = _________________
∴R=
T
273
R = 8
...
In M
...
S
...
314 Joule K mol
1 calorie = 4
...
987 cals deg mol
9
...
Partial
pressure is the measure of the pressure of an individual gas in a mixture of
same volume and temperature
...
are the partial pressures of the various gases
present in a mixture, then the total pressure P of the gaseous mixture is
given by
P = p1 + p2 + p3
...
Equation of state of a Gaseous mixture
Let a gaseous mixture consists of nA, nB and nC moles of three ideal
gases A, B and C respectively, subjected to constant T and V, then,
according to ideal gas equation
...
Hence the total pressure of the mixture is given as
P = pA + pB + pc
200
nART
____
P =
V
nBRT
nCRT
____ + ____
+
V
V
∴ PV = (nA + nB + nC) RT
This equation is known as equation of state of gaseous mixture
...
__
RT
___
...
e:-
xA = mole fraction of A
...
Similarly;
pB = XB P
Thus, the partial pressure of the individual component in the mixture
can be calculated by the product of its mole fraction and total pressure
...
201
number of moles of N2
____________________
pN2 =
V
x
RT
number of moles of H2
pH2 = ____________________
V
x
RT
2
Mole fraction of N2 = XN2
2
___
=
4
∴ XH2
= _____
2+2
= 0
...
5 (XN2 + XH2 = 1
...
For 1 mole, V = 22
...
4 litres and
R = 0
...
0821 x 273
P = __________
4 x 22
...
2501 x 0
...
2501 x 0
...
2501 atm
...
1251 atm
= 0
...
T
...
[Ans: pO2 = 0
...
0625 atm]
202
9
...
This is
due to the movement of molecule of one gas into the other gas
...
In 1829, Graham formulated what is now known as Graham's law of
diffusion
...
Mathematically the law can be expressed as
r1
M2
=
r2
M1
where r1 and r2 are the rates of diffusion of gases 1 and 2, while M1 and M2
are their molecular masses respectively
...
The rate of diffusion of a gas also
depends on the molecular mass of the gas
...
It may be expressed
mathematically as
Effusion rate of Gas 1
Effusion rate of Gas 2
=
M2
M1
The determination of rate of effusion is much easier compared to the
rate of diffusion
...
Problem 2
If a gas diffuses at the rate of one-half as fast as O2, find the molecular
mass of the gas
...
203
1
r1
M2
=
;
r2
M1
2 =
1
32
M1
Squaring both sides of the equation
2
1
__
2
32
1
32
__ (or) __ = __
=
M1
4
M1
M1 = 128
Thus the molecular mass of the unknown gas is 128
...
Find the
molecular mass
...
The same
volume of CO2 under identical conditions effuse in 115 seconds
...
Effusion rate of CO
Effusion rate of A
50
50
115 =
146
MA = 71
MA
44
2 =
MA
M
CO
2
; (1
...
Self Test
75ml of gas A effuses through a pin hole in 73 seconds
...
Calculate
the molecular mass of A
...
6)
204
9
...
Real gases do not obey the perfect gas equation exactly
...
Repulsive forces between the molecules cause
expansion, and attractive forces cause reduction in volume
...
At other conditions of pressure and volume,
deviations are seen
...
This postulate
holds good for ideal gases and only under normal conditions of temperature
and pressure for real gases
...
In such cases, the
volume occupied by the gaseous molecules cannot be neglected in
comparison with total volume of the gas
...
9
...
Pressure deviation
For an ideal gas the forces of attraction between the gaseous molecule
are considered to be nil at all temperature and pressure
...
Under these conditions, the volume of the gas is high and the
molecules lie far apart from one another
...
But at high pressure (or) at low temperature, the volume of the gas is
small and molecules lie closer to one another
...
Therefore it is
necessary to apply suitable corrections to the pressure of the real gas in the
equation of state
...
7 Vanderwaal's Equation of state
For an ideal gas PV = nRT, is considered as the equation of state
...
O Vanderwaal's deduced the equation of state of
real gases
...
Volume V of an ideal gas is the same as the volume
of the container
...
If Vm is the volume
of the single molecule then, the excluded volume which is termed as "b" is
determined as follows
...
9
...
9
...
The space
indicated by dotted sphere of radius 2r will not be available for other
molecules to freely move about
...
e) the dotted spherical volume is known
as excluded volume per pair of the molecules
...
∴ The excluded volume for n molecules, 'b' = 4n Vm, where 4 Vm is the
excluded volume of a molecule
...
ii) Pressure Correction
In a real gas the pressure deviation is caused by the intermolecular
forces of attraction
...
Consider a molecule placed in the interior of the
container
...
However a molecule
near the wall of the container which is about to strike is surrounded
unequally by other gaseous molecules as shown in Fig 9
...
Fig
...
5
Intermolecular forces of attraction and pressure deviation in
real gas molecules
The molecule near the wall experiences attractive forces only such that
it will strike the wall with a lower force which will exert a lower pressure
than if such attractive forces are not operating on it
...
The corrected pressure should be P + p' where p' is
the pressure correction factor
...
It is
found experimentally that, p' is directly proportional to the square of the
density of the gas (ρ) which is a measure of the intermolecular attraction of
the molecules
...
e)
n
where ρ = __
V
P′
...
Therefore P′ of one mole of the gas is
given by
1
P′
...
∴ corrected pressure = P + P′
a
__
= P +
V2
Replacing the term for corrected volume and the corrected pressure in
the ideal gas equation for one mole, the equation of state of the real gas is
a
P + __
V2
(V-b) = RT
where `a' and `b' are known as vanderwaal's constants
...
If there are `n' moles of the real gas then the vanderwall's equation
becomes
n2a
P + ___
V2
(V-nb) = nRT
209
Units for vanderwaal's constant
The dimensions of the vanderwaal's constant a and b depend upon the
units of P and V respectively
...
(Volume)2
= ________________
mole2
a
= atm
...
dm6 mol-2 units
...
The term a/V2 is the measure of the attractive forces of the molecules
...
2
...
The vanderwaal constants `a' and `b' enable the calculation of critical
constants of a gas
...
32 litre
at 48°C and at a pressure of 16
...
Calculate the pressure of the gas that
would have been expected to behave ideally and non-ideally
...
59 atm dm6 mol-2];
4
...
082 dm3 atm deg-1
...
32 lit
48 + 273 = 321 K
0
...
atm K-1
...
082 x 321
__ = __________
P =
V
1
...
94 atm
For real behaviour,
RT
a
___
__ (n = 1 mole)
P =
−
V-b
V2
0
...
32 - 0
...
59
______
(1
...
6 - 2
...
54 atm
Limitations of Vanderwaal's equation
1
...
2
...
3
...
211
9
...
When a gaseous system is transformed to its liquid state, there is a
tremendous decrease in the volume
...
In both these effects the gaseous molecules come
closer to each other and experience an increase in force of attraction which
results in liquefaction of gases
...
Such P-V curves at
constant temperature are known as isotherms
...
9
...
The figure 9
...
There is a definite deviation
exhibited by the real gas from ideal gas behaviour at high pressure and low
volumes
...
For instance Tc of CO2
is 31
...
This means that it is not possible to liquefy CO2 by applying
pressure when its temperature is above 31
...
Critical pressure (Pc)
It is defined as the minimum pressure required to liquefy 1 mole of a
gas present at its critical temperature
...
A gas is said to be at its critical state when its pressure, volume and
temperature are Pc, Vc and Tc
...
8
...
The isotherm of carbondioxide
determined by him at different temperatures are shown in Fig
...
6
...
9
...
1°C
...
On increasing the pressure its volume diminishes
as is indicated by the curve AB
...
At C, the
gas becomes completely liquefied
...
This is shown by a steep
line CD which is almost vertical
...
Along BC, it exists in equilibrium between gaseous and liquid
state
...
The isotherm at 21
...
Therefore more pressure is applied to
213
decrease the volume
...
1°C
...
1°C it reduces to a point
...
1°C is regarded as the critical temperature of CO2
...
Above 31
...
CO2 cannot be liquefied above 31
...
The portion of area covered by curve H with zyx portion
always represents the gaseous state of CO2
...
8
...
He
suggested that there should be no sharp points in the isotherms below the
critical temperature
...
This, he showed as a theoretical wavy
curve
...
9
...
The curve MNC represents a superheated liquid
because compression above Tc, leads to heating effects
...
The Vanderwaal's equation may be written
as
P +
a
__
V2
(V-b) = RT
expanding the expression,
a
ab
PV − Pb + __ − __ − RT = 0
V
V2
Multiplying by V2
PV3 − (RT + Pb) V2 + aV − ab = 0
214
Fig
...
7
Thomson's isotherms of CO2
Thus, for any given values of P and T there should be three values of V
...
The
three values of V become closer as the horizontal part of the isotherm rises
...
Here,
the gas is said to be in critical state
...
9
...
3
Derivation of critical constants from Vanderwaal's constants
Let us derive the values of critical constants Tc (critical temperature), Vc
(critical volume) and Pc (critical pressure) in terms of the Vanderwaal's
constants `a' and `b'
...
At
the critical point, the three values of V become identical and is equal to the
critical volume (Vc)
...
RTc
V − ___ + b
Pc
3
aV
ab
__
__ = 0
V +
−
Pc
Pc
2
(8)
Equating the powers of V from equation
216
−3 Vc V
RTc
= − ___ + b
Pc
3 Vc
= b
RTc
+ ___
Pc
3 Vc2
a
= __
Pc
(10)
Vc3
ab
__
=
Pc
(11)
2
Vc3
___
3Vc2
(9)
ab
Pc
___
...
Since Pc and Tc can often
be determined experimentally, these values may be employed to calculate
the constants a and b
...
H2, N2, He,
...
Gases like NH3, CO2,
SO2, HCl etc
...
Problem 5
Vanderwaal's constants for hydrogen chloride gas are a = 3
...
8 ml mol-1
...
218
Solution
8a
____
Tc =
27Rb
8 x 3
...
0821 x 0
...
7 K
= 51
...
67
___ = ___________
Pc =
27 x (0
...
6 atm
Problem 6
The critical temperature of hydrogen gas is 33
...
4 atm
...
Solution : We know
8a
a
Tc = ____
...
(ii)
Dividing (i) by (ii) we get
8a
Tc
__ = ____
Pc
27Rb
x
27b2
____
a
8b
__
...
2°C = 33
...
2K and Pc = 12
...
082
atm
...
Substituting the values in equation (iii), we get
306
...
4
0
...
2 x 0
...
4 x 8
=
0
...
Now, substituting the value of `b' in equation (i) we have
8a
8xa
Tc = ____ (or) 306
...
082 x 0
...
439 atm litre2 mol-1
9
...
The phenomenon of producing lowering of temperature when a gas is
made to expand adiabatically from a region of high pressure into a region of
low pressure, is known as Joule - Thomson effect
...
In
this case work is done by the gas molecules at the expense of internal
energy of the gas
...
This
reduction in the temperature is generally referred as Joule-Thomson effect
and is used in the liquefaction of gases
...
10
Inversion temperature (Ti)
The Joule-Thomson effect is obeyed by a gaseous system only when its
temperature is below a characteristic value
...
Ti is characteristic of a gas and it is related to the Vanderwaal's constant
`a' and `b',
2a
Ti = __
Rb
220
At the inversion temperature there is no Joule Thomson effect (ie) there
is neither fall nor rise in temperature
...
If the temperature of the gas is above Ti there is a
small rise in temperature
...
These gases will
obey Joule-Thomson effect only when they are cooled to a temperature
below these Ti values
...
11
Conditions of liquefaction of gases
Many industrial processes require large quantities of liquid air, liquid
ammonia, liquid carbondioxide etc
...
There are different methods of liquefaction of gases, such as (i) based
on the concept of critical temperature followed by the compression
(ii) based on Joule-Thomson effect (iii) Adiabatic demagnetisation
...
Gases like H2, O2, N2 and He have very low Tc values and hence Joule
Thomson effect may be applied to bring in effective cooling
...
Linde's Method
This method makes use of Joule Thomson effect and is used to liquify
air or any other gas
...
10
...
The valve v of jet J is then opened and the gas is
allowed to expand suddenly into the wider chamber C
...
9
...
The gas is now allowed to pass through the outer tube `O'
...
Further
cooling of the incoming gas occurs during expansion in the chamber C
...
By repeating the
process of cooling and compression followed by expansion, the gas is
liquefied and finally the liquid air drops out from the jet into the bottom of
chamber C
...
This work is done at the expense of the kinetic energy of the gas
and hence a fall of temperature is noted
...
Air is compressed to about 200 atmospheres and is passed through the pipe
ABC (Fig
...
9)
...
Here the air moves the piston outwards and expands in volume
as a result of which considerable cooling is produced
...
The precooled incoming compressed air then
experiences Joule-Thomson expansion when passed through Jet nozzle J
222
and gets cooled further
...
Fig
...
9 Claude's apparatus for liquefaction of air
Adiabatic demagnetisation
Generally, the method used to reach the very low temperature of about
10 K is adiabatic demagnetisation
...
The paramagnetic sample used in this method is suddenly
magnetised by the application of strong magnetic field
...
When
the magnetic field is suddenly removed, demagnetisation occurs which
brings in a disordered state of the molecular magnets
...
By this technique, as low as zero kelvin can be
reached
...
Choose the correct answer :
1
...
This
shows relationship between
1
(a) P and ___
(b) PV and V
V
1
(c) P and V (d) V and ___
P
3
...
4
...
(a) Number of molecules of the gas decreases
(b) The kinetic energy of the molecules decreases
(c) The kinetic energy of the molecules decreases
(d) The kinetic energy of the molecules increases
5
...
The ratio of molecular weight (MA/MB)
will be
1
1
(a) ___
(b) 4 (c) ___
(d) 16
16
4
B
...
The correction term for pressure deviation is ……in the Vanderwaal
equation of state
...
The relation between inversion temperature and Vanderwaal’s
constants `a’ and `b’ is
method is exclusively used
...
To liquefy Helium
9
...
The rate of diffusion of gas is
to square root of both
and molecular mass
...
Match the following
A
11
...
Adiabatic
demagnetization
13
...
1oC
14
...
Ratio of the partial
pressure to the total
pressure
B
(a) Critical temperature
(b) Liquid oxygen
(c) Mole fraction of the gas
(d) Number of moles of
the gas
(e) Low pressure and high temperature
(f) Liquid Helium
D
...
Write the mathematical expression for Boyle's law
...
Compare the partial pressures of gases A and B when 3 moles of A and
5 moles of B mixed in constant volume, and 25oC and 1 atm pressure
...
Give the correction factors for the volume and pressure deviation for a
Vanderwaal's gas
...
A sample of an ideal gas escapes into an evacuated container, there is
no change in the kinetic energy of the gas
...
What is the change in temperature when a compressed real gas is
allowed to expand adiabatically through a porous plug
...
Define Boyle's law and Charle's law
...
What are measurable properties of gases?
23
...
Define Graham's law of diffusion
...
Give the values of R-gas constant in calories and Joules
...
What are the units of Vanderwaals constants `a' and `b' ?
27
...
28
...
29
...
30
...
Explain briefly on the following
31 At 27oC, H2 is leaked through a tiny hole into a vessel for 20 minutes
...
After effusion of the gas, the
mixture exerts a pressure of 6 atm
...
7
moles
...
Also report the pressure of gas if it
behaves ideally in nature
...
592 atm lit2 mol-2
...
0427 lit mol-1
Ans
...
2 atm
= 131
...
Calculate the total pressure in a 10 L cylinder which contains 0
...
6 g of oxygen and 1
...
Also calculate
the
partial pressures of He gas in the cylinder
...
R = 0
...
Ptotal = 0
...
2463 atm
...
1231 atm,
pN2 = 0
...
The critical constants for water are 374oC, 218 atm and 0
...
Calculate `a' and `b' of water
...
a
b
= 2
...
0189 lit mol-1
35
...
6 and b = 4
...
Calculate the critical temperature and
critical volume of the gas
...
0820 lit atm K-1
...
Explain the causes for deviation for real gases from ideal behaviour
...
Deduce the relationship between critical constants and Vanderwaal's
constants
...
Describe Linde's process of liquefaction of gases with neat diagram
...
Describe Claude's process of liquefaction of gases with neat diagram
...
What is meant by adiabatic demagnetisation? Explain its use in
liquefaction of gases
...
They obey
Boyle's and Charle's law
...
•
For constant mass of a gas,
P1V1
____
T1
•
P2V2
____
=
T2
Different units of R :0
...
314 x 107 erg K-1 mol-1;
8
...
987 cal K-1 mol-1
...
•
By Graham's law, (diffusion rate1/diffusion rate2) = (M2/M1)½ (or)
(effusion rate1/ effusion rate2) = (M2/M1)½
•
Real gases deviate from Videal and Pideal
...
P +
a
__
2
(V-b) = RT for n = 1
...
Andrew's isotherm describes critical
temperature of carbondioxide
...
Pc, Vc, Tc are related to Vanderwaal's constants a and b as Vc = 3b;
a
____;
Pc =
27b2
Tc =
8a
____
27Rb
227
•
Joule Thomson effect predicts adiabatic expansion of a compressed gas
through an orifice to cause a fall in temperature
...
•
Liquefaction of gases is carried out by Linde's and Claude's processes
adopting Joule-Thomson effect
...
REFERENCES :
Text book of physical chemistry, Lewis and Glasstone
Title: Chemistry
Description: This note is for 100 level students this note will guide you in everything about chemistry
Description: This note is for 100 level students this note will guide you in everything about chemistry