Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

2nd secondary

1

Chemistry
Second Secondary

2nd secondary

2

Contents
Chapter One:
Atomic structure
...
youtube
...

https://www
...
com/watch?v=hePb00CqvP0

Chapter Three:
Bonds and forms of molecules
...
youtube
...

https://www
...
com/watch?v=-0N1ZZZRM48

2nd secondary

3

General objectives of chapter one:
1-Recognize the historical background of atomic structure
...

3-Discuss the Rutherford’s atomic model
...

5-Define the reasons of inadequacy of Bohr’s model
...

7-Explain the concept of electron cloud and orbitals
...

9-Distribute electrons of any atom considering the building
up principle and hund’s rule
...


2nd secondary

4

Chapter one

Structure of the atom
Atomic structure
1-Democritus’s (Greek philosophers) idea:
Any piece of matter can be divided into smaller parts and each part can be
subdivided into smaller parts which can't be divided this part is called Atom
...

b- He supposed that all matters composed of 4 constituents which are (water,
air, dust and fire) and postulated that the cheap metals such as iron or copper
can be changed into precious ones like gold by changing the percentage of four
constituents
...

B-He was the 1st scientist to define the element as pure simple substance which
Cannot be analyses into simple one by normal chemical methods
...

2- Every element consists of very small dense atoms which can’t be divided
...

4- Atoms of different are different
...


5 – Thomson’s model of the atom:
The scientist Thomson carried out many experiments on the electric
discharge through gases from which he had discovered the cathode rays
...


2nd secondary

5

Cathode- rays experiment
(Discovery of the electron)
High voltage 10000
vollts

Anode

Cathode
To vacuum pump

a- All gases under normal conditions of pressure and temp
(76 cm
...
25c) don't conduct electricity
...
These rays were named by (Cathode rays)
...

2) Transfers in straight lines glowing the glass facing the cathode
...

4) Have a thermal effect
...

6) Cathode rays don’t change by changing either cathode material or type
of the gas, which proves that cathode rays take part in the structure of
all substances
...


2nd secondary

6

Metal sheet covered
with ZnS

Gold foil
Source of alpha
particles

1– He allowed alpha particles to hit a metallic plate lined with Zinc sulphide
(glows when hits with alpha rays)
2– On placing a gold foil in the front of alpha rays he concluded the
following from the following observation
...

1- A very small percentage of alpha
particles reflected back to
appears as flashes on other side of
sheet
...


2- Most of the atom is a space not
solid as explained by Dalton
and Thomson
...

4- The dense parts of the atom,
which concentrate in it most
mass, have same charge of
alpha particle (+ve) which
called nucleus of the atom
...


1- The Atom:
Although it has very small size but it has a complicated structure that
resembles the solar system in which electrons revolve around the
central nucleus in orbits as planets revolve around the sun
...
Located in the centre of the atom with
(+ve) charge
...
Most mass of the atom is
concentrated in the nucleus as mass of e is very small and can be
neglected
...

2- No of electrons (-ve) equals no of protons (+ve) so the atom is
electrically neutral
...

b- Centrifugal force due to velocity of electron around the nucleus
...

Explain: Structure of the atom in the view of Rutherford
...

2- Atom is electrically neutral as no of p+ s equals to no of e's
...

4- Electrons orbit the nucleus in a rapid movement without gaining or losing
energy
...


2nd secondary

8

6- Each electron in the atom has a definite amount of energy depending on
the distance between is E
...
This energy increases as its radius
increases
...
Each level has energy expressed by a completely no called principle Q
...


Ex: The 1st E
...
no = 1
The 2nd E
...
no = 2
8- If when atom is excited by heating (Quantum) or by electric discharge
the electron will transfer to a higher E
...
The excited electron in the higher E
...


 Remarks:
1- The quantum: Is the amount of energy gained or lost when an electron
jumps from one E
...

2- The difference in energy between levels (Q) is not equal i
...
the difference in
this energy decreases further from the nucleus
...

3- The electron does not move from its level to another unless the energy
absorbed or emitted is equal to the difference in energy between 2 levels i
...

one quantum
...
Q can't be divided or doubled

Give reason: It is wrong to say that e' to be transferred from E
...
L (M)
needs amount of energy equals 2 quantum
...
L to higher ones
...

2- He introduced the idea of quantum no to detect energy of electrons in
energy levels
...


Disadvantages (Inadequacies) of Bohr's theory:
1 – If failed to explain the spectrum of any other element even that of He
except hydrogen (Simplest Electronic System)
...

3– He postulated that it is possible to determine precisely both speed and
location of an electron at the same time
...

4– He described the electron when moving in a circular planer orbit, which
means that hydrogen atom is planer
...


Bohr's Theory
The atomic spectrum
Studying and explaining the atomic spectrum was the key to his atomic
structure in 1913 and he was deserved Noble Prize in 1922
...

2 – By using spectroscope we find that this light consists of a fixed number of
colored lines called line spectrum
...


2nd secondary

10

By exp
...


N
...


The principles of Modern Atomic Theory:
1 – Dual nature of electron
...

3 – Finding the mathematical expression, which describes the wave motion
of electron, its shape and its energy?
-------------------------------

1 – The dual nature of the electron
The experimental data showed that the electron has a dual nature i
...

a) It is a material particle
...


* De Broglie principle:
Every moving body (such as electron or the nucleus of an atom or whole
molecule) is associated with (accompanied by) a wave motion (or matter
waves) which has some properties of light waves
...
We can only say that it is
probably to a greater r lesser extent to locate the electron in this or in that
place
...

3
...

 The electronic motion around nucleus has wave properties therefore the
position to use the term electron cloud to describe any orbital
...
"
 The difference between the orbit and orbital concepts according to both
Bohr and the wave mechanics theories:
Bohr s theory
Schrodinger s wave mechanics theory
 It is a circular planer orbit with
 It is an electron cloud used to
particular radii
describe any orbital
 Electron cloud the regions of
high density of dots represent
the region of high probability of
finding the ( e ) from which it is
Bohr's orbit
possible to define the atomic
radius
Probabili
ty of
finding
the
electron

Schrodinger's wave mechanics
theory

Distance from
the nucleus
R

Probabilit
y of
finding
the
electron
Distance from the
nucleus

2nd secondary

12

 The mathematical solution of the Schrodinger equation introduced four
numbers which are called quantum numbers
...
Besides, they define the energy, shape
and direction of orbital
...
no (n)
...
no (ℓ)
...
no (mℓ)
...
no (ms)
...
levels their number in the heaviest known atom in
the ground state is seven
...
level = two times the square of
the level no (2n2)
...
L
K
Is filled with
2 electrons
nd
-2 E
...
L
M
Is filled with
18 electrons
th
-4 E
...
However,
the atom becomes unstable if no of electrons exceeds 32 electrons on any
level
...
Subsidiary Q No (ℓ):
1- Used to detect the no of sub levels in each E
...

2- The energy sub levels take the symbols s, p, d, f
...
When he used a spectroscope, which has a high resolving
power, he found that the single line (which represents electron transition
between two different energy levels) is indeed a number of fine spectral
lines which represents electron transition between very near energy
levels (sublevels)
...


-1st E
...
L
-3rd E
...
L

K
L
M
N

has 1 sub level
has 2 sub level
has 3 sub level
has 4 sub level

1s
2s, 2p
3s, 3p, 3d
4s, 4p, 4d, 4f

N
...
level is not equal
...
levels also differ in energy
...


Ex: 4d>3d

4p>3p>2p

 There is a small difference in the energy between sub-levels
...
Magnetic Q No (m):
Detected by Zeeman when he exposed spectral line to strong magnetic field, he
found that each line divides into many lines, so he concluded that each E
...


- Magnetic Q No(mℓ ) is characterized by:
1- Used to detect no of orbitals in each E
...

2- Sublevel (S) has one orbital of spherical symmetrical shape
...

 Each orbital (Px,Py,Pz ) is perpendicular to the other two
...
e point of zero electron
y
density
...

5- Sublevel (f) has 7 orbital
...

Ex: px = py = pz
7- No of orbitals in each E
...
level = n2
...
No (ms):

 Detects the direction in which the electron spins around its axis during its
rotation around the nucleus
...

 It has only two possible values + 1/2 – 1/2




Give reason: Each orbital carries 2 electrons although they are negatively
charged
...
L, sub levels
orbitals and no of electrons:
1- No of energy sublevels = order of principle level (n)
...
, while the formula of ammonia is
...
no
...

3- The oxidation number of oxygen in most of its compounds is
...
While in the elementary state is
...
But in
metal hydroxide is ……………
...
of
ionization potential and electron affinity
...

2- Elements of valence shell filled by more than its half
...

4-They are element oxides that react with acids as basic oxides and react with
bases as acidic oxides forming in both cases salt and water
...
Orbitals, it can accommodate up to

...

(2 - 3 - 5 - 10 - 14)
2- An element of atomic number 10, the number of sublevels filled with
electrons are
...

a) np4
b) np5
c) np
d) np3
4- Group 5-A elements are classified as
...
(S-P-d-f)

2nd secondary

36

5- Sublevel (f) saturated with number of electrons equals
...

a) 8
b) 16
c) 32
d) 64
7- Electron affinity in group decrease
...

9- The oxidation number of the first group elements equal
...

a) +2
b) +l
c)-2
d)-l
11- The electron affinity of Fluorine as compared to chlorine is
...

a) 2+
b)4+
c)2d) 6+
14- The metallic property increase in the group elements by
...

b) Increasing of ionic potential
...

d) When the radius decrease
...
The radius of Al is smaller than that of Na in the same period
...
The oxidation number of elements of the first group (1A) in the periodic
table is (1+)
...
Cesium is considered the most active metal
...
P - Sublevel saturated with 6 electrons
...


Physically,
of the atom
...
Line spectra is characteristic for any element
...
Quantum numbers can not used to find the number of electrons in energy
level more than 4
...
Elements of S, P blocks called representative elements
...
Element of f block are called inner transition elements
...


2nd secondary

38

General objectives of chapter three:
At the end of this chapter, the student shoud be able to:
1- Construes why atoms tend to form chemical bonds
...

3- Define the type of bond on the basis of electronegativity
...

5- Explain the inadequacies of the octet rule
...

7- Recognize the concept of hybridization
...

9- Compare between sigma and pi bonds
...


2nd secondary

39

Chapter three
Chemical reaction
Chemical reaction:

 Is the reaction in which the bonds of reactants are broken forming
new bonds in products?
 (Inert gases are chemically inactive)
...
P
...
A
...


Because: There is no chemical bond formed between iron and Sulphur
...


Types of bonds:
A-Chemical bonds:
1) Ionic bond
...


2) Covalent Bond
...

2) Metallic bonds
...
It is known
that atoms of metals are characterized by large volumes (atomic radius)
...
This facilitates the loss of
their few electrons of the outermost shell
...


2nd secondary

40

- On the other hand, nonmetal atoms are characterized by their small
volumes
...
Non-metal atoms are changed to
anions with an identical electron structure to the nearest noble gas in the
periodic table
...
It is called the ionic bond
...


Examples: Formation of NaCl:
Na
2, 8, 1

Na+ + e2, 8

Na+ + Cl -

NaCl

Cl + e2, 8, 7

Cl2, 8, 8

- Ionic bond is formed between atoms when the difference in E
...
7
- As the difference in E
...
between atoms increases, the strength of the
ionic bond increases which increases the melting point, boiling point and
degree of conductivity
...
9
Nacl
3-
...
1
810
1465

1
...
2=1
...
5
Alcl
3-1
...
5
190
Changing directly
from solid to gas
(sublimes)
Does not conduct
(covalent bond)

Cl
3

2nd secondary

41

General properties of ionic compounds:
(1) Structure:
- These are crystals that are constructed of collections of cations and
anions bound by electrostatic forces in crystal lattice containing the ion
in a regular pattern
...


II- covalent Bond:
- Formed between atoms of non-metals of the same element (have the
same Electronegativity) or between atoms of different elements have
difference in E
...
less than 1
...
N (difference in E
...
N
...
Thus, the electron pair spends the same time
in the vicinity of each atom and the net charge on each atom is zero
...
N less than 1
...
N
...
e
...
As a result, chlorine atom
acquires a partial negative charge (-δ) and not complete one (as in the
case of chloride ion Cl-), while hydrogen atom acquires a partial positive
charge (+δ)

---