1. Chemistry Form 4 Chapter 2 – Atom Structure
CHEMISTRY – study of composition, structure, properties and interactions of matter.
REMEMBER DEFINITIONS!
MATTER – anything that occupies space and has mass, made up of tiny and discrete particles.
ATOM – the smallest particle of an element that can participate in a chemical reaction.
MOLECULE – group of two or more atoms chemically bonded together.
ION – positively charged or negatively charged particle
DIFFUSION – movement of particles of a substance in between the particles of another
substance
Fixed vol + shape Fixed vol, shape of No fixed vol or shape
No compress container Easy compress
Packed close and Compress is hard Far apart in random
ordered Packed close, not motion
Strong force ordered Weak force between
between particles Force between particles
Vibrate and rotate particles weaker Vibrate, rotate, move
in fixed position than solid’s freely, more collision
Vibrate, rotate,
move through
liquid, collide
MELTING – when solid is heated, particles gain kinetic energy(k.e) and vibrate faster. As temp
goes up, k.e goes up until overcomes forces holding them together. Solid becomes liquid.
Temperature when this happens is melting point.
FREEZING – when liquid is cooled, particles lose k.e and vibrate slower. When particles don’t
have enough energy to move freely, liquid becomes solid. Temperature when this happens is
freezing point.
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2. Chemistry Form 4 Chapter 2 – Atom Structure
The melting point graph
Graph to the left shows heating of substance
X. At a, X is solid.
As it is heated, a→b, heat energy is absorbed,
the particles gain k.e. and vibrate faster, increasing
temp.
At b (MoC), X begins to melt, but the temp is
constant, because the heat absorbed is used to
overcome strong forces to become liquid. From b→c,
X is solid‐liquid.
At c, X is melted and turned fully liquid.
At c→d, the particles absorb heat as in a→b.
The Freezing Point Graph
Graph to the left shows cooling of substance X.
At d, X is liquid.
As X cools, d→e, particles lose k.e, vibrate
slower and drops temp.
At e (FoC), X begins to freeze, but temp. is
constant, because heat loss to surroundings is balanced
by heat released by particles turning to solid. From e→f,
X is liquid‐solid.
At f, X is frozen and turned fully solid.
At f→g, particles lose heat as in d→e.
~The Atomic Structure~
John Dalton’s small, indivisible atom model.
J.J. Thomson’s positive sphere
with negative electrons atom model.
© Amir Fuhaira 2008‐20XX. Nak guna boleh, nak copy minta izin. Kalau tak boleh blah.

3. Chemistry Form 4 Chapter 2 – Atom Structure
Ernest Rutherford’s atom model. Protons and
most of atom’s mass in nucleus with electrons
moving around it.
Neils Bohr proposed shells in
which electrons move around the nucleus.
James Chadwick showed that nuclei have neutrons, a
neutral particle, which is about half of the atom’s
mass.
Subatomic Particles
Atoms have 3 subatomic particles. In atom, no of electrons = no of protons.
Electron
Mass is 0.0005 of a proton.
Electrical charge = ‐1
Proton Neutron
Mass is 1x proton. Mass is 1x proton.
Electrical charge = Electrical charge = 0
+1
Proton, Nucleon Number and Element Symbol
PROTON NUMBER is the number of protons in an atom = electron number in atom.
NUCLEON NUMBER is the number of protons + neutrons in an atom.
Symbol of elements: (where X is element, A is nucleon, Z is proton)
You can also denote elements as (element‐nucleon) – Ex: Sodium‐23, Chlorine‐35, etc.
© Amir Fuhaira 2008‐20XX. Nak guna boleh, nak copy minta izin. Kalau tak boleh blah.

4. Chemistry Form 4 Chapter 2 – Atom Structure
Isotopes and importance
Isotopes are atoms with same proton number and different neutron number. Eg: Hydrogen‐1,
Hydrogen‐2 (Deuterium) and Hydrogen‐3 (Tritium).
Isotope Uses:
Cobalt‐60 : Cancer treatment in radiotherapy
Cobalt‐60 : Gamma rays to destroy food bacteria
Carbon‐14 : Carbon dating to determine age of fossils and artifacts.
Phosphorus‐32 : Study of plant metabolism of phosphorus using P‐32 fertilizers
[ atom electronic structure ]
Atoms with proton numbers 1‐20 obey these shell limits.
First shell: 2 electrons
Second shell: 8 electrons
Third shell: 8 electrons
Outermost shell’s electron number is Valence Electron.
© Amir Fuhaira 2008‐20XX. Nak guna boleh, nak copy minta izin. Kalau tak boleh blah.