This document discusses the structure of atoms. It defines key terms like atoms, molecules, and ions. Atoms are made up of subatomic particles like protons, neutrons, and electrons. The document traces the historical development of atomic models from Dalton to Chadwick. Isotopes are defined as atoms of the same element with different numbers of neutrons. Examples of isotopes in hydrogen and chlorine are given. Uses of isotopes in medicine, agriculture, and other fields are outlined. The electronic structure of atoms is explained using the example of chlorine's 2.8.7 configuration and defining valence electrons.

1. Chapter 2
The Structure of the Atom

2. 2.1 Matter
• Matter: Anything that occupies space and has
mass
• Based on theory: Matter is made up of tiny and
discrete particles. There are spaces between
these particles
• Types of particle:
 Atoms
 Molecules
 Ions

3. • Atom: The smallest particle of an element that can
participate in a chemical reaction
• Molecule: A group of two or more atoms which are
chemically bonded together
• Ion: A positively-charged or negatively-charged
particle

4. • Diffusion: Occurs when particles of a
substance move in between the particles of
another substance
• Diffusion of matter occurs most rapidly in
gases, slower in liquids and slowest in solids →
due to the different arrangement and
movement of particles
• Observe this video

5. Kinetic Theory of Matter
• Types of matter:
 Solid
 Liquid
 Gas

6. The arrangement and movement of particles
in solid, liquid and gas are described in the
kinetic theory of matter.

7. The Change in The State of Matter
Sublimation
Sublimation
Condensation
Boiling /
Evaporation
Melting
Freezing

8. When solid is heated;
• The particles in the solid gain kinetic energy and
vibrate more vigorously.
• The particles vibrate faster as the temperature
increases until the energy they gained is able to
overcome the forces that hold them at their fixed
positions.
• At this point, the solid becomes a liquid.
• This process called melting.
• The temperature at which this happens is called
melting point.

9. When liquid is heated;
• The particles in the liquid gain kinetic energy
and move faster.
• The particles move faster as the temperature
increases until the energy they gained is able
to overcome the forces that hold them.
• At this point, the liquid becomes a gas.
• This process is called boiling.
• The temperature at which this happens is
called boiling point.

10. When liquid is cooled;
• The particles in the liquid lose energy and
move slower.
• As the temperature decreases, the particles
lose more energy until they did not have
enough energy to move freely.
• At this point, the liquid changes into a solid.
• This process is called freezing.
• The temperature at which this happens is
called freezing point.

11. Definition:
• Melting point
The temperature at which a solid changes into
a liquid at a particular pressure.
• Freezing point
The temperature at which a liquid changes
into a solid at a particular pressure.

12. The heating curve
Temperature (°C)
Time (min)
Melting
point
A
B C
D
solid
begin
to melt
liquid
solid-liquid
The temperature remains constant because:
The heat energy absorbed is used to overcome the
force attraction between particles so that solid can
change into liquid
Heat energy is absorbed.
Particles in solid gain kinetic energy and
vibrate faster
Heat energy is absorbed.
Particles in liquid gain kinetic energy and
move faster

13. The cooling curve
Temperature (°C)
Time (min)
Freezing
point
E
F G
H
liquid
solid
liquid-solid
The temperature remains constant because:
The heat loss to the surrounding is equal to the heat
energy formed during particles attraction to form a
solid
Heat energy is released.
Particles in liquid lose kinetic energy
and move slower
Heat energy is released.
Particles in solid lose kinetic energy and
vibrate slower

14. 2.2 The Atomic Structure
Historical development of atomic models
Model Structure Characteristic
Dalton’s atomic model
proposed by John
Dalton in 1805
The atom was
imagined as a small
indivisible ball similar
to a very tiny ball.
Thomson’s atomic
model proposed by J.J.
Thomson in 1897
J.J Thomson
discovered electron, a
negatively-charged
particle.
The atom was
described as a sphere
of positive charge
embedded with
electrons.

15. Model Structure Characteristic
Rutherford’s atomic
model proposed by
Ernest Rutherford
in 1911
Ernest Rutherford
discovered proton,
a positively-charged
particle in an atom.
The central region
of atom has a very
small positively-
charged nucleus,
which contains
almost all the mass
of the atom.
Bohr’s atomic
model proposed by
Neils Bohr in 1913
The electrons in an
atom move in shells
around the nucleus
which contains
protons.

16. Model Structure Characteristic
Chadwick’s atomic
model proposed
by James Chadwick
in 1932
Chadwick proved
the existence of
neutrons, the
neutral particle in
the nucleus.
The nucleus of the
atom contains
protons &
neutrons, and the
nucleus is
surrounded by
electrons.

17. Subatomic particles in atom
 Proton
 Neutron
 Electron
Subatomic particles

18. Relative electric charge: +1
Relative mass: 1
Relative electric charge: 0
Relative mass: 1
Properties of subatomic particles
Nucleus
Proton, p
Neutron, n
Relative electric charge: -1
Relative mass: ≈ 0.0005
Electron, e

19. Proton number and nucleon number
 Proton number:
The number of proton in its atom
** also shows the number of electrons in the
atom
 Nucleon number:
The total number of protons and neutrons in its
atom
** also known as mass number

20. What is the relationship??
Nucleon
number
Proton
number
Number of
neutrons= +
Nucleon
number
Number of
protons
Number of
neutrons= +
OR

21. Reminder!!!
Proton number
Nucleon number
Neutron number
√
√
X
Number of neutron

22. Symbol of elements
X
A
Z
Nucleon
number
Proton
number
Symbol of
element

23. 2.3 Isotopes and Their Importance
Isotopes:
• Atoms of the same element with same
number of proton but different number of
neutrons.
OR
• Atoms of the same element with same proton
number but different nucleon number.

24. Example of elements with isotopes:
• Hydrogen
H
1
1 H
2
1 H
3
1
Hydrogen-1 Hydrogen-3Hydrogen-2

25. • Chlorine
Cl
35
17 Cl
37
17
Chlorine-35 Chlorine-37

26. Uses of isotopes in our daily lives
In the medical field:
• Cobalt-60
Used in radiotherapy for the treatment of cancer
• Iodine-131
Treatment of thyroid gland
In the argiculture field:
• Phosphorus-32
Study the metabolism of phosphorus in plants
• Gamma ray of cobalt-60
Used to destroy bacteria in food

27. Uses of isotopes in our daily lives
In industrial field:
• Sodium-24
Used detect leakages in pipes
In archeology field:
• Carbon-14
To estimate the age of fossils and artifacts

28. 2.4 The Electronic Structure of an Atom
The first shell : 2 electrons
The second shell : 8 electrons
The third shell : 8 electrons
Nucleus

29. Example:
Chlorine atom
• Proton number of 17
• Hence, chlorine atom has 17 electrons
• Electron arrangement:
2.8.7

30. Valence electrons
• The electrons in the outermost occupied shell
Outermost
occupied shell
Valence electron