Explain how an ionic bond is formed between sodium and chlorine atoms.

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

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

Sodium has one electron in its outer shell. Chlorine has seven electrons in its outer shell.

Model answer (4 marks)

Sodium gives its single outer‑shell electron to chlorine.

The loss of an electron makes sodium a +1 ion (Na⁺).

Chlorine gains the electron, giving it a –1 charge (Cl⁻).

The oppositely charged ions are attracted by electrostatic attraction, forming an ionic bond.

Examiner tips

Use the word ‘transfer’ or ‘give’ to show electron movement. Mention the charges (+1, –1) explicitly. Explain that attraction between opposite charges creates the bond. Keep the answer concise – one sentence per point.

Common mistakes

Writing that sodium *gains* an electron or chlorine *loses* one. Forgetting to state the charges of the ions. Using vague terms like ‘bond’ without describing the electrostatic attraction.

Mark scheme (4 marks)

Sodium transfers/loses one electron to chlorine
Sodium forms a positive ion (Na⁺) because it loses a negative charge
Chlorine forms a negative ion (Cl⁻) because it gains a negative charge
The oppositely charged ions are attracted to each other by electrostatic attraction

Key terms in this question

ionic bond · ion