# Silicon dioxide (SiO₂) is used to make glass and optical fibres. It has a very high melting point and does not conduct electricity. Explain the properties of silicon dioxide in terms of its giant covalent structure.

> OCR A-Level Chemistry A (H432) — 2.4 Electrons, bonding and structure · Explain · 5 marks

> Silicon dioxide is a giant covalent structure used widely in industry. Unlike metals or ionic compounds, it behaves very differently when heated or when a voltage is applied.

## Mark scheme (5 marks)

1. Silicon dioxide contains many atoms held together by covalent bonds
2. The covalent bonds are strong
3. A large amount of energy is needed to break these strong covalent bonds
4. This explains the high melting point of silicon dioxide
5. Silicon dioxide does not conduct electricity because it has no delocalised electrons (or free ions) to carry charge

## Key terms

- [giant covalent structure](https://www.gradenine.co.uk/glossary/giant-covalent-structure)
- [melting point](https://www.gradenine.co.uk/glossary/melting-point)

## Related

- [Revision notes for OCR A-Level Chemistry A (H432)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/silicon-dioxide-sio-is-used-to-2273a28c) · Published by Druglandscape Ltd.