F4 Chapter 8 topic 8.2

8.2 Modern Periodic Table
of Elements

8.2.1 The Principle for the Arrangement of the Elements
in the Modern Periodic Table of Elements

• Period = 7 horizontal rows of elements
• Group = 18 vertical columns
• Bottom: Two series elements with the proton numbers of 57 to 71

and 89 to 103 placed separately

• Moving from left to right across a period – gradual change in
chemical and physical properties:
• Decrease in metallic properties, increase in non-
metallic properties
• Change of the properties of oxides from basic to
acidic
• Decrease in chemical conductivity

• Elements are arranged from left to right and top to bottom in the
order of their increasing proton number



Proton • Proton number: 2 (number of
Neutron
Electron proton in the nucleus is 2)
• Neutron number: 2 (number
Helium atom
of neutron in the nucleus is 2)
• Nucleon number: 4 (number

of proton + neutron in the

nucleus is 4)

• Proton number = number of proton in a nucleus of an atom
• Neutron number = number of neutron ilangan neutron in the

nucleus of an atom
• Nucleon number = number of proton and neutron in the nucleus

of an atom

8.2.2 Electron Arrangements of the Elements

• For a neutral atom, number of proton = number of electron
• Electrons are arranged in shells around the nucleus

• Electrons occupy the shells closest to the nucleus first
• Electrons then start occupying a new shell when the previous

one has been occupied

: 2 electrons
: 8 electrons
: 18 electrons

Nucleus

Example: Sulphur

• Sulphur atom has a proton number of 16 = 16 electrons
• 2 electrons: in the first shell
• 8 electrons: second shell
• Remaining 6 electrons in the third shell (valence)

8.2.3 Formation of Positive and Negative Ions

• Most atoms have unstable electron arrangement – tends to form a
stable electron arrangement

• Neutral atoms form ions:
I. Donating the outermost electrons to other atoms (positive
ions) OR
II. Accepting the outermost electrons of the other atoms
(negative ions)

• To achieve a stable duplet or octet electron arrangement

Duplet electron Octet electron
arrangement arrangement
= stable electron = stable electron
arrangement with 2 arrangement with 8
electrons in the first electrons in the
shell outermost shell

Example 1: Magnesium
Donates 2 electrons

Magnesium atom (Mg) Magnesium ion (Mg2+)
Electron arrangement: 2.8.2 Electron arrangement: 2.8

• Magnesium atom has 12 electrons (2.8.2)
• To achieve a stable octet arrangement, it is easier to donate 2

electrons (than accepting 6 electrons)
• Positive ion formed by donating electrons

Example 2: Chlorine

Accepts 1 electron

Chlorine atom (Cl) Chloride ion (Cl-)
Electron arrangement: 2.8.7 Electron arrangement: 2.8.8

• Chlorine atom has 17 electrons (2.8.7)
• To achieve a stable octet arrangement, it is easier to accept 1

electron from another atom (as compared to donating 7 electrons

to other atoms
• Negative ion formed by accepting electrons