# Explain why ionic compounds such as sodium chloride have high melting points but do not conduct electricity when solid, yet do conduct electricity when melted.

> OCR GCSE Chemistry A: Gateway Science (J248) — C2.3 Properties of materials · Explain · 4 marks

> Sodium chloride is an ionic compound used widely in food preservation and the chemical industry. Its electrical behaviour changes dramatically depending on its physical state.

## Mark scheme (4 marks)

1. Ionic compounds are held together by strong electrostatic forces (between oppositely charged ions)
2. A large amount of energy is needed to overcome these strong electrostatic forces, hence the high melting point
3. In the solid state the ions are held in fixed positions and cannot move, so charge cannot be carried
4. When melted the ions are free to move and can carry charge, allowing electrical conduction

## Key terms

- [ionic compound](https://www.gradenine.co.uk/glossary/ionic-compound)
- [ion](https://www.gradenine.co.uk/glossary/ion)
- [melting point](https://www.gradenine.co.uk/glossary/melting-point)

## Related

- [Revision notes for OCR GCSE Chemistry A: Gateway Science (J248)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-ionic-compounds-such-as-cd01df58) · Published by Druglandscape Ltd.