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2nd secondary

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Chemistry
Second Secondary

2nd secondary

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Contents
Chapter One:
Atomic structure
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youtube
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https://www
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com/watch?v=hePb00CqvP0

Chapter Three:
Bonds and forms of molecules
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youtube
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https://www
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com/watch?v=-0N1ZZZRM48

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General objectives of chapter one:
1-Recognize the historical background of atomic structure
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3-Discuss the Rutherford’s atomic model
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5-Define the reasons of inadequacy of Bohr’s model
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7-Explain the concept of electron cloud and orbitals
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9-Distribute electrons of any atom considering the building
up principle and hund’s rule
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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
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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
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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
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2- Every element consists of very small dense atoms which can’t be divided
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4- Atoms of different are different
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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
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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
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25c) don't conduct electricity
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These rays were named by (Cathode rays)
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2) Transfers in straight lines glowing the glass facing the cathode
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4) Have a thermal effect
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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
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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
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1- A very small percentage of alpha
particles reflected back to
appears as flashes on other side of
sheet
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2- Most of the atom is a space not
solid as explained by Dalton
and Thomson
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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
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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
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Located in the centre of the atom with
(+ve) charge
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Most mass of the atom is
concentrated in the nucleus as mass of e is very small and can be
neglected
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2- No of electrons (-ve) equals no of protons (+ve) so the atom is
electrically neutral
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b- Centrifugal force due to velocity of electron around the nucleus
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Explain: Structure of the atom in the view of Rutherford
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2- Atom is electrically neutral as no of p+ s equals to no of e's
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4- Electrons orbit the nucleus in a rapid movement without gaining or losing
energy
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6- Each electron in the atom has a definite amount of energy depending on
the distance between is E
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This energy increases as its radius
increases
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Each level has energy expressed by a completely no called principle Q
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Ex: The 1st E
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no = 1
The 2nd E
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no = 2
8- If when atom is excited by heating (Quantum) or by electric discharge
the electron will transfer to a higher E
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The excited electron in the higher E
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 Remarks:
1- The quantum: Is the amount of energy gained or lost when an electron
jumps from one E
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2- The difference in energy between levels (Q) is not equal i
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the difference in
this energy decreases further from the nucleus
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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
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one quantum
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Q can't be divided or doubled

Give reason: It is wrong to say that e' to be transferred from E
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L (M)
needs amount of energy equals 2 quantum
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L to higher ones
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2- He introduced the idea of quantum no to detect energy of electrons in
energy levels
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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)
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3– He postulated that it is possible to determine precisely both speed and
location of an electron at the same time
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4– He described the electron when moving in a circular planer orbit, which
means that hydrogen atom is planer
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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
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2 – By using spectroscope we find that this light consists of a fixed number of
colored lines called line spectrum
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By exp
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N
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The principles of Modern Atomic Theory:
1 – Dual nature of electron
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3 – Finding the mathematical expression, which describes the wave motion
of electron, its shape and its energy?
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1 – The dual nature of the electron
The experimental data showed that the electron has a dual nature i
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a) It is a material particle
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* 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
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We can only say that it is
probably to a greater r lesser extent to locate the electron in this or in that
place
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3
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 The electronic motion around nucleus has wave properties therefore the
position to use the term electron cloud to describe any orbital
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 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

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 The mathematical solution of the Schrodinger equation introduced four
numbers which are called quantum numbers
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Besides, they define the energy, shape
and direction of orbital
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no (n)
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no (ℓ)
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no (mℓ)
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no (ms)
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levels their number in the heaviest known atom in
the ground state is seven
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level = two times the square of
the level no (2n2)
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L
K
Is filled with
2 electrons
nd
-2 E
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L
M
Is filled with
18 electrons
th
-4 E
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However,
the atom becomes unstable if no of electrons exceeds 32 electrons on any
level
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Subsidiary Q No (ℓ):
1- Used to detect the no of sub levels in each E
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2- The energy sub levels take the symbols s, p, d, f
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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)
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-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
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levels also differ in energy
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Ex: 4d>3d

4p>3p>2p

 There is a small difference in the energy between sub-levels
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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
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- Magnetic Q No(mℓ ) is characterized by:
1- Used to detect no of orbitals in each E
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2- Sublevel (S) has one orbital of spherical symmetrical shape
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 Each orbital (Px,Py,Pz ) is perpendicular to the other two
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e point of zero electron
y
density
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5- Sublevel (f) has 7 orbital
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Ex: px = py = pz
7- No of orbitals in each E
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level = n2
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No (ms):

 Detects the direction in which the electron spins around its axis during its
rotation around the nucleus
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 It has only two possible values + 1/2 – 1/2




Give reason: Each orbital carries 2 electrons although they are negatively
charged
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L, sub levels
orbitals and no of electrons:
1- No of energy sublevels = order of principle level (n)
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3- No of electrons occupying a given E
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Ex:
Order of E
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E
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These rules are:
 Pauli’s exclusion principle : it states that:
 It is impossible for two electrons in the same atom to have the same four
quantum numbers
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Ex: 4s is filled before 3d as energy of 4s < 3d
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Ex:
8O

2
2
3
7N 1s – 2s – 2p

px py py
2p   
2s 

1s 

1s

2s


1s2 – 2s2 – 2p4

2p


px


py


py


 Atom is stable when the outer sub-level is half completely filled with e's
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2- Electrons prefer to be paired with another electron than to transfer to a
higher sub-level, as the energy needed to transfer it to a higher sub-level
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Other E
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Write short notes on:
1- Hund's rule
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3- Heisenberg uncertainty principle
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Write scientific term:
1- Area of space around nucleus which has probability for finding electron
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3- Sublevel can be saturated with 10 electrons
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number which detects no of orbitals and their direction in space
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number used to detect direction of electron around its axis
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Complete:
1- Max
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The electrons can be distributed in
…………
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levels …………
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orbitals
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In energy
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and ………
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Give reason:
1- It’s wrong to consider the electron as (-ve) particle only
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3- The relation 2n2 cannot be applied to O, P and Q levels
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5- Sub level d is filled with 10 electrons
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(First question):

20

A- Choose the correct answer:
1- The energy sublevels that form the third energy level are --------a- s

b- s, p

c- s, p, d

d- s, p, d, f

2- The uncertainty principle was proposed by-----------------a- Heisenberg
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C- Rutherford
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3- The --------elements tend to reach the electron structure : ns2 , np6
a- Main transition
b- inner transition
c- noble

d- transition

B- Give reasons:
1- The atomic radius in the same group increases as the atomic number increases
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C- Write the electronic configuration for 20 Ca by two different ways and show
the location of element in modern periodic table

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