# Explain why metals are better thermal conductors than non-metals, and why gases are poor thermal conductors.

> Cambridge International IGCSE Physics (0625) — 2.3 Transfer of thermal energy · Explain · 4 marks

## Mark scheme (4 marks)

1. In metals, free (delocalised) electrons transfer heat energy through the lattice
2. This makes metals good conductors because free electrons transfer energy rapidly
3. In non-metals, heat is transferred only by lattice vibrations passed between neighbouring atoms
4. In gases, particles are far apart so collisions are infrequent, making energy transfer inefficient

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