1. The document discusses the history of the atomic model from Democritus' idea of atoms in 400 BC to Chadwick's discovery of neutrons in 1932. 2. Key developments included Dalton's atomic theory in 1805, Thomson's discovery of electrons in 1897, Rutherford's nuclear model in 1910, and Bohr's model of electron orbits in 1913. 3. The document also covers atomic structure, including the properties and configuration of subatomic particles like protons, neutrons, and electrons.

1. S.MORRIS 2006

3. HISTORY OF THE ATOMHISTORY OF THE ATOM
400 BC Democritus develops the idea of atoms
he pounded up materials in his pestle and
mortar until he had reduced them to smaller
and smaller particles which he called
ATOMAATOMA
(greek for indivisible)

4. HISTORY OF THE ATOMHISTORY OF THE ATOM
1805 John Dalton : Atomic Theory, atoms of same
element are alike
suggested that all matter was made up of
tiny spheres that were able to bounce around
with perfect elasticity and called them
ATOMSATOMS

5. HISTORY OF THE ATOMHISTORY OF THE ATOM
1897 Joseph John Thompson
found that atoms could sometimes eject a
far smaller negative particle which he called
an
ELECTRONELECTRON

6. HISTORY OF THE ATOMHISTORY OF THE ATOM
1910 Ernest Rutherford
Rutherford’s new evidence allowed him to
propose a more detailed model with a central
NUCLEUS.
He suggested that the positive charge was all
in a central nucleus which is the PROTON.
With this holding the electrons in place by
electrical attraction

7. HISTORY OF THE ATOMHISTORY OF THE ATOM
1913 Niels Bohr
Bohr refined Rutherford's idea by adding
that the electrons were in orbits. Rather
like planets orbiting the sun. With each
orbit only able to contain a set number of
electrons.

8. Bohr’s Model
electrons in orbits
nucleus

9. HISTORY OF THE ATOMHISTORY OF THE ATOM
1932 James Chadwick
Discovers NEUTRONS

10. ATOMIC STRUCTUREATOMIC STRUCTURE
Particle
proton
neutron
electron
Charge
+ ve charge
-ve charge
No charge
1
1
nil
Mass

11. ATOMIC STRUCTUREATOMIC STRUCTURE
HeHe
the number of protons and
neutrons in an atom
44 Mass number/Nucleon number
the number of protons in an atom
22 Atomic number/Proton number
number of electrons = number of protons

12. HELIUM ATOM
+
N
N
+
-
-
proton
electron neutron
Shell
What do these particles consist of?

13. QuestionQuestion
Write the number of protons, electrons and neutrons
for the following elements;
O
Cl Si
NaCa
20
40
11
23
8
17
16
35
14
28
B
11
5
a) b)
c)
d) e) f)

14. Relative Atomic Mass
• Ar : it is the average mass of naturally
occurring atoms of an element on a scale
where the carbon- 12 atom has a mass of
exactly 12 units.
• It is the mass number of an atom
• Example: has a mass of 40Ca
20
40

15. Relative Molecular Mass
• Mr : it is the sum of the relative atomic
masses of the atoms in a compound
• Example: CO2
has an Mr of
(12 x 1) + (16 x 2) = 44

16. Relative Molecular Mass
Diffusion of HCl and NH3
:
Find the Mr of the reagents.

17. Relative Formula Mass
• Mr : it is the sum of the relative atomic
masses of the atoms in an ionic
compound
• Example: NaCl has a formula mass of
(23 x 1) + (35.5 x 1) = 58.5

18. ATOMIC STRUCTUREATOMIC STRUCTURE
There are two ways to represent the atomic
structure of an element or compound;
1. Electronic Configuration
2. Dot & Cross Diagrams

19. ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION
With electronic configuration elements are represented
numerically by the number of electrons in their shells
and number of shells. For example;
Nitrogen has seven electrons, so, its electronic
configuration is: 2 . 5

20. ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION
Maximum number of electrons in each shell: 2n2
Where, n is the shell number (1,2,3,….)
N
Nitrogen
7
2 in 1st
shell
5 in 2nd
shell
configuration = 2 , 5
2 + 5 = 7

21. ATOMIC STRUCTUREATOMIC STRUCTURE
Electrons are arranged in Energy Levels or
Shells around the nucleus of an atom.
• first shell a maximum of 2 electrons
• second shell a maximum of 8 electrons
• third shell a maximum of 18 electrons

22. ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION
Write the electronic configuration for the following
elements;
Ca O
Cl Si
Na
20 11 8
17 14
B
5
a) b) c)
d) e) f)
2,8,8,2 2,8,1
2,8,7 2,8,4 2,3
2,6

23. DOT & CROSS DIAGRAMSDOT & CROSS DIAGRAMS
With Dot & Cross diagrams elements and compounds
are represented by Dots or Crosses to show electrons,
and circles to show the shells. For example;
Nitrogen N XX X
X
XX
X
N7
14

24. DOT & CROSS DIAGRAMSDOT & CROSS DIAGRAMS
Draw the Dot & Cross diagrams for the following
elements;
O Cl8 17
16
35
a) b)
O
X
X
X
X
X
X
X
X
Cl
X
X
X
X X
X
X
X
X
X
X
X
X
X
X
X
X

25. Dot and Cross DiagramsDot and Cross Diagrams
Draw the dot and cross diagrams for the following
elements;
Ca O
Cl Si
Na
20 11 8
17 14
B
5
a) b) c)
d) e) f)
2,8,8,2 2,8,1
2,8,7 2,8,4 2,3
2,6

26. The Atom Helium
ElectronProton
Neutron
Helium has two electrons, two protons and two neutrons

27. The Atom Lithium
Protons
Neutrons
Electrons
Lithium has three electrons, three protons and four neutrons

28. The Atom Beryllium
Protons
Neutrons
Electrons
Beryllium has four electrons, four protons and five neutrons.

29. The Atom Boron
Protons
Neutrons
Electrons
Boron has five electrons, five protons and six neutrons.

30. The Atom Carbon
Protons
Neutrons
Electrons
Carbon has six electrons, six protons and six neutrons.

31. The Atom Nitrogen
Protons
Neutrons
Electrons
Nitrogen has seven electrons, seven protons and seven neutrons.

32. The Atom Oxygen
Protons
Neutrons
Electrons
Oxygen has eight electrons, eight protons and eight neutrons.

33. The Atom Fluorine
Protons
Neutrons
Electrons
Fluorine has nine electrons, nine protons and ten neutrons.

34. The Atom Neon
Protons
Neutrons
Electrons
Neon has ten electrons, ten protons and ten neutrons.

35. The Atom Sodium
Protons
Neutrons
Electrons
Sodium has eleven electrons, eleven protons and twelve neutrons.

36. Ion
• An ion is a charged particle. It can be an
atom, or a molecule. Example, Na+
, Ca2+
,
NH4
+
, CO3
2-
, Cl -
, O2-
• In an ion, number of protons is not equal
to the number of electrons
• When a particle loses an electron, it
becomes positively charged. When it
gains electron, it becomes negatively

39. Valency
• Valency is the number of electrons a
particle donates or accepts in order to
form a compound
• It is the value of the charge in an ion
• Example, the valency of Na+
is +1 and the
valency of O2-
is -2

40. Radical
• a radical is a group of atoms which can
combine with another element as a single
unit.
• Example, NH4
+
is a radical and its valency
is +1

41. Isotopes
• Atoms of the same element having the
same proton number but different nucleon
number, due to different number of neutrons
• Example, Chlorine has two isotopes, Cl-35
and Cl- 37
• Hydrogen has three isotopes, H-1, H-2 and
H-3

42. Isotopes : Hydrogen

43. Isotopes: Carbon

44. Isotopes: Chlorine

45. SUMMARYSUMMARY
1. The Atomic Number of an atom = number of
protons in the nucleus.
2. The Atomic Mass of an atom = number of
Protons + Neutrons in the nucleus.
3. The number of Protons = Number of Electrons.
4. Electrons orbit the nucleus in shells.
5. Each shell can only carry a set number of electrons.