GCSE Combined Science revision · Chemistry: atoms, bonding and amounts

Ionic and covalent bonding

The idea

Ionic bonding happens between metals and non-metals: electrons transfer from the metal to the non-metal, forming ions with full outer shells. Ionic compounds form giant lattices held by strong electrostatic forces between oppositely charged ions. Covalent bonding happens between non-metals: atoms share pairs of electrons. Covalent substances can be small molecules (water, methane), giant structures (diamond) or polymers.

Metal + non-metal: ionic. Non-metals only: covalent.
Show electron transfer or sharing with a dot-and-cross diagram.
Work out the formula from the ions' charges.

Watch out In ionic bonding electrons are transferred, not shared.

See it worked

Worked example

Describe how magnesium and oxygen form magnesium oxide.

Each magnesium atom loses two electrons to form Mg²⁺.
Each oxygen atom gains two electrons to form O²⁻.
The ions attract strongly, forming a giant lattice.

Answer Magnesium transfers two electrons to oxygen, forming Mg²⁺ and O²⁻ ions

Your turn

Question 1Calculator allowed1 mark

What is the formula of the compound formed from Ca²⁺ and Cl⁻ ions?

Question 2Calculator allowed1 mark

Which substance has covalent bonding?

Question 3Calculator allowed1 mark

What holds a giant ionic lattice together?

In past papers

89 official questions in 47 papers since 2018. The latest:

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