1. 2.2 Atomic Structure
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John Dalton (1808) proposed that:All elements are made of atoms
Atoms neither created or destroyed
Atoms of the same element are alike and differ
from different element
When atoms are combined, they do so in a
simple ratio
Chemical reactions will results in combination or
separation of atoms

2. 2.2 Atomic Structure
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J.J Thompson (1897) :Discovered negatively
charged particles called
electrons.
Suggested that atom is
positively charged sphere
with electrons embeded
inside it

3. 2.2 Atomic Structure
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Ernest Rutherford (1911) :Suggested that most of the atom must be empty
space
Proposed that all the positive charge is
concentrated in nucleus.
Named the positively charged particles as
protons
Proposed that an atom is a positively charged
nucleus with a cloud of electrons surrounding it.

4. 2.2 Atomic Structure
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Neils Bohr (1913) proposed that:Electrons in the atom are arranged in permitted
orbits called electron shells surrounding the
nucleus
James Chadwick (1932) :Discovered neutrons; neutral subatomic
particles.
Neutron has mass almost the same as proton.
Suggested that nucleus of atom contain proton
and neutrons.

5. 2.2 Atomic Structure
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Proton Number :Number of proton in atom of an element
Also known as atomic number
Proton number also tell us the number of
electrons.
Eg:- Magnesium atom has 12 protons, thus it
has 12 electrons.

6. 2.2 Atomic Structure
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Nucleon Number :The sum of protons and neutrons in its atom
Also known as relative mass
Eg:- A sodium atom has 11 protons and 12
neutrons. Hence the nucleon number or relative
mass is 23.

7. 2.2 Atomic Structure
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Symbols of element :Each element is represented with a symbol
It may represented by the first letter of its name.
Eg:- Hydrogen  H, Nitrogen  N
Some is represented with a second letter added
after its initial to differentiate between other
elements. Eg:- Nickel  Ni
Some are represented by its Latin name. Eg:Silver = Argentum  Ag.

8. 2.3 Isotopes and their importance
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Isotopes :Atoms of the same element with the same proton
number but different nucleon numbers or same elements
with same number of protons but different number of
neutrons
Have same chemical properties but different physical
properties such as density and melting point
Eg:- Cl-35, Cl-37.
Unstable isotopes are radioactive isotopes which will
undergo spontaneous decay to emit radioacctive rays.
Eg:- Cobalt-60

9. 2.4 The Electronic Structure of an Atom
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Electron arrangement in atom :Quantum orbit@ electron orbits.
First shell are filled first with max of 2 electrons
The remaining electrons are filled in the next
shell with max of 8 electrons
The remaining electrons then are filled into the
third shell and can take a max of 8 to 18
electrons
The way the electrons are distributed are called
electron arrangement