1.6 Ionic Bonding

REVISION NOTES

IGCSE Edexcel Chemistry

1.6.1 Understand how ions are formed by electron loss or gain

IONS

Ions are formed when atoms gain or lose electron(s)
In order to form full electron shells (octet rule)
- So that it can be more stable

Metals tend to lose electrons → forming positive ions (cations)
Nonmetals tend to gain electrons → forming negative ions (anions)

Formation of Cations (Metal Losing Electrons)

Formation of Anions(Nonmetal Gaining Electrons)

1.6.2 Know the charges of these ions:

Metals in Groups 1, 2 and 3
Non-metals in Groups 5, 6 and 7
Ag⁺, Cu²⁺, Fe²⁺, Fe³⁺, Pb²⁺, Zn²⁺
Hydrogen (H⁺), Hydroxide (OH^–), Ammonium (NH₄⁺), Carbonate (CO₃^2–), Nitrate (NO₃^–), Sulphate (SO₄^2–).

Metals and Nonmetals in Group 1, 2, 3, 5, 6 and 7:

Transition metals: Ag⁺, Cu²⁺, Fe²⁺, Fe³⁺, Pb²⁺, Zn²⁺

Common Groups (Polyatomic Ions):

1.6.3 Write formulae for compounds formed between the ions listed above

IONIC COMPOUNDS

Ionic compounds are formed when a positive ion combines with a negative ion
The net charge of an ionic compound is 0
- Number of ions should be multiplied to make sure the sum of charge = 0
- Cross-multiply each ion with the charge of the other ion
It can be applied to common groups (polyatomic ions) as well

EXAMPLE

What is the formula of aluminium sulphate?

Al is in group III

→ charge = 3+

→ Al³⁺

Sulphate is a common ion

→ SO₄^2-

1.6.4 Draw dot-and-cross diagrams to show the formation of ionic compounds by electron transfer, limited to combinations of elements from Groups 1, 2, 3 and 5, 6, 7 only outer electrons need be shown

Ionic compounds are formed when there is electron transfer between metals and nonmetals

Metals lose electrons
Nonmetals gain electrons

Key points

Electron(s) gained by the nonmetal should be annotated by a different symbol than the symbols of electrons in the nonmetal
After ions are formed, there should be square bracket and charge on the top right corner

EXAMPLE

Draw the dot-and-cross diagram to show the formation of the compound CaO

1.6.5 Understand ionic bonding in terms of electrostatic attractions

IONIC BONDING

Electrostatic attraction force between two oppositely charged ions
Exact terminologies should be memorised

1.6.6 Understand why compounds with giant ionic lattices have high melting and boiling points

STRUCTURE OF IONIC COMPOUNDS

Ionic compounds are giant lattice structure of ions
Due to the strong electrostatic attraction forces, ionic compounds have high melting and boiling points
Ionic compounds are usually solid at room temperature and are non-volatile
They are usually water soluble as both ionic compounds and water are polar substances