# Explain why silicon dioxide (SiO₂) has a very high melting point and does not conduct electricity.

> AQA A-Level Chemistry (7405) — 3.1.3 Bonding · Explain · 5 marks

> Silicon dioxide is used to make glass and is found in sand. It is a solid at room temperature with a melting point above 1600 °C.

## Mark scheme (5 marks)

1. Silicon dioxide has a giant covalent structure (giant lattice / macromolecular structure)
2. Each silicon atom is bonded to oxygen atoms by strong covalent bonds throughout the structure
3. A large amount of energy is needed to break these strong covalent bonds
4. Silicon dioxide does not conduct electricity because it has no free (delocalised) electrons
5. Silicon dioxide does not conduct electricity because it has no mobile ions (in the solid or liquid state)

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