Aluminium oxide is an ionic compound. Describe how aluminium and oxygen atoms form ions and explain what holds the ions together in the ionic compound.

Cambridge International IGCSE Chemistry (0620) — 2.4 Ions and ionic bonds · Describe and Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Aluminium atom loses 3 electrons to give Al³⁺ ion.
Oxygen atom gains 2 electrons to give O²⁻ ion.
The atoms therefore become oppositely charged ions.
The ionic bond is the electrostatic attraction between the Al³⁺ and O²⁻ ions.

Examiner tips

Use the exact charge symbols (Al³⁺, O²⁻) and state the electron transfer. Explain that the attraction is electrostatic. Keep the answer concise – one sentence per point.

Common mistakes

Writing Al⁺ or O⁻ instead of the correct charges. Forgetting to mention the electron transfer. Using vague terms like "strong bond" instead of "electrostatic attraction".

Mark scheme (4 marks)

Aluminium atom loses 3 electrons to form Al³⁺ ion
Oxygen atom gains 2 electrons to form O²⁻ ion
Oppositely charged ions are formed (one positive, one negative)
The ionic bond is the electrostatic attraction between the oppositely charged ions

Key terms in this question

ion