# Silicon dioxide is a giant covalent structure. Explain why silicon dioxide has a high melting point and does not conduct electricity in any state.

> Pearson Edexcel International GCSE Chemistry (4CH1) — 1.7 Covalent substances · Explain · 4 marks

> Silicon dioxide is used to line furnaces and as an electrical insulator in high-temperature applications. Each silicon atom is covalently bonded to four oxygen atoms, and each oxygen atom is covalently bonded to two silicon atoms throughout the structure.

## Mark scheme (4 marks)

1. Silicon dioxide contains many strong covalent bonds throughout the structure
2. A large amount of energy is needed to break these covalent bonds, so the melting point is high
3. There are no free/delocalised electrons in silicon dioxide
4. Therefore there are no charged particles free to move to carry electrical charge/current

## Key terms

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

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