Notesale: Turn your study into money

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Matter
All the objects that we see in the world around us, are made of matter
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Scientists discovered that matter is made up of particles which can be atoms,
molecules or ions
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1
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An atom is the smallest unit
of an element that can participate in a chemical change
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An element consists of only one type of atom, which has a mass that is characteristic of the
element and is the same for all atoms of that element
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3
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In a given compound, the numbers of atoms of each of its elements are always present
in the same ratio
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Atoms are neither created nor destroyed during a chemical change, but are instead rearranged
to yield substances that are different from those present before the change
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Number one postulate is no longer acceptable because radioactive elements are dividing
spontaneously
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226
88

2
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Isotopy is a
phenomenon that occurs when an element can exist in two or more forms having similar
chemical properties but different atomic masses
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Both have the same number of electrons in their outermost shells
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3
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The changes that occur as a result of atomic fission, destroy
atoms of the element involved
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The nucleus of the uranium isotope U=235, can absorb a
neutron and break up into two unequal atoms with mass numbers of 95 and 140
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Number four theory is still acceptable for most elements in inorganic chemistry
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Atomic Theory
Atom
An atom is the smallest particle of an element, which can take part in a chemical reaction
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Molecule
A molecule of a compound or element is the smallest particle of a compound or element which is
capable of independent existence
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For example, a nitrogen molecule (N2) contains two atoms of
nitrogen, an oxygen molecule (O2) contains two atoms of oxygen but a molecule of water (H2O)
contains two atoms of hydrogen and one atom of oxygen
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It is formed as a result of the loss or
gain of electrons
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There are two
types of ions
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A cation is formed when an atom or group loses electrons
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An anion is formed when an atom or group gains electrons
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If an atom gains or loses an electron or electrons, it
becomes an ion
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Atomicity:
Atomicity of an element is the number of atoms in one molecule of the element
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g copper (Cu), sodium
(Na)
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g O2
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Element whose molecule contains four
atoms
are said to be tetra-atomic while a molecule containing more than four atoms is said to be
polyatomic eg S8
ELEMENT

MOLECULAR FORMULA

ATOMICITY

Sodium

Na

1

Hydrogen

H2

2

Nitrogen

N2

2

Ozone

O3

3

Phosphorus

P4

4

Sulphur

S8

8

Atomic structure
As a result of the models that we discussed in section 3
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This knowledge is important because it helps us to understand things
like why materials have different properties and why some materials bond with others
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So far, we have discussed that atoms are made up of a positively charged nucleus surrounded by
one or more negatively charged electrons
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The Electron
The electron is a very light particle
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11 x 10−31 kg
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The electron also carries one unit of negative electric charge which
is the same as 1
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The Proton
Each proton carries one unit of positive electric charge
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e
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The total positive charge of a nucleus is equal to the number of protons in the nucleus
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6726 x
10−27 kg
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Like the proton, it is much
heavier than the electron and its mass is 1
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Rutherford predicted (in 1920) that another kind of particle must be present in the nucleus along
with the proton
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However, it is
actually, four times heavier than hydrogen
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To make sure that the atom stays electrically neutral,
this particle would have to be neutral itself
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Unlike the electron which is thought to be a point particle and unable to be broken up into
smaller pieces, the proton and neutron can be divided
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The proton and neutron are made up of 3 quarks each
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602 × 10-

nucleus

19

Nucleus

−1
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00055

24

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1
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00091 × 101
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00866

1
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The different isotopes of an element have the same atomic number Z but different mass numbers
A because they have a different number of neutrons N
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Note
that if an element is written for example as C-12, the ’12’ is the atomic mass of that atom
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ample
Atomic number
The chemical properties of an element are determined by the charge of its nucleus, i
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by the
number of protons
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Definition: Atomic number (Z) The number of protons in an atom
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The total number of
protons plus neutrons, is called the atomic mass number and is denoted by the letter A
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The number of neutrons
is simply the difference N = A − Z
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For example, the
symbol for
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It is the combining power or
capacity of an element or radical
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Elements having a single valency are said to be monovalent, while those with
two valencies are said to be divalent
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Copper, for example, is a divalent element with valencies of 1 and 2
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A chemical formula is a short
hand method of representing a compound
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A chemical formula of a compound tells us:
i
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ii
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Binary Compounds:
Binary compounds are compounds containing only two elements and they always end in (ide) e
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When two or more elements
combine chemically to form a compound, the valency of each element will tell us the number of
atoms of X that will combine with Y:
Question 1:
If X has valency of +1 and Y has valency of 1,
both X and Y have equal valences
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H = +1, O = -2 Formula of water = H2O
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Al = +3, O = -2
The formula of aluminum oxide is Al2O3
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When a metal combines with a
radical, a salt is formed
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It indicates the types of atoms present and the simplest whole-number ratio of
the number of atoms (or ions) in the compound
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What is the empirical formula of an organic compound, which contains 80% Carbon and 20%
hydrogen
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(C = 12, H = 1)
80

Ration of carbon present in the compound =12 = 6
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7: 20, divide both number by the smaller one
6
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7

:

20
6
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Given that the sample of a compound contains 8
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3 g

of hydrogen and 10
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(H = 1, C = 12, O = 16)
Solution
Let calculate the mole of each element present
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3
1
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3
8

Carbon = 12 = 0
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7

Oxygen = 16 = 0
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67: 1
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67
Divide through by the smallest value
= 1:2:1
Molecular Formular
Molecular formular of a compound is a whole number multiple of its empirical formula
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Molecular formula is derived from the empirical formula of the
compound
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What is the molecular formula of a compound, which on analysis, its empirical formula is
found to be CH2 and its relative molecular mass is known to be 42
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The relative molecular mass = 42
CH2 = 12 + (1x2) = 14
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𝑅𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝑚𝑎𝑠𝑠

=
𝑓𝑜𝑟𝑚𝑢𝑙𝑎 𝑚𝑎𝑠𝑠
...
42
14

=3

The molecular formula of the compound is 3 x CH2 = C3H6
4
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0g of carbon, 0
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67g of
Oxygen
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(C = 12, H = 1, O = 16)
Let calculate the mole of each element present in the compound’
2

C = 12 = 0
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34

O=

2
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34

= 0
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17: 0
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17
Divide through by the smallest value
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Molecular mass of the compound is 180
(CH2O)n = 180
Cn + H2n + On = 180
12n + 2n + 16n = 180
30n = 180

n=

180
30

=6

n=6
Multiple the empirical formula by 6 and the molecular formula is (CH2O)6 = C6H12O6
5
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(H = 1, C = 12, O = 16)
Solution
We have to apply the relation
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6
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If the percentage composition of carbon in the compound is 89
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(H = 1, C = 12)
Solution As usual, the very first step is to calculate the number of moles of each element:
n=
For carbon we have
m = 89
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6
12

Substituting we have
n = = 7
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6 g = 10
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4
1

Substituting we have
n = 10
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42 moles
C = 1, H = 1
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4 to 1, then we have to multiply the above mole ratio
by 5 to obtain
C=5
H=7
Thus, the empirical formula of lycopene is C5H7
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The relative molecular mass of aspartame, an artificial sweetener containing carbon, hydrogen,
oxygen and nitrogen, is 294g
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3% and 9
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(H = 1, C = 12, N = 14, O = 16)
Solution
We must first work out the number of moles of the constituent
elements:
n=
For carbon we have
m = 57 g
M = 12 g/ mole
57

n = 12
Substituting we have
n = = 4
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3 g
M = 16 g/ mole
27
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71 mole
For nitrogen we have
m = 9
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7

n = 14

Substituting we have
n = = 0
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693 mole:
C=7
H=9
N=1
O = 2
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5 to 3, we have to multiply each number by 2 to
obtain
C = 14
H = 18
N=2
O = 16
Thus, the empirical formula of aspartame is C14H18N2O5
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