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 · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

In metals, free (delocalised) electrons can move through the lattice and transfer kinetic energy rapidly, making them good conductors.
In non‑metals, heat is carried only by lattice vibrations (phonons) that must pass between neighbouring atoms, so conduction is slower.
In gases the particles are far apart; collisions are infrequent, so energy transfer by collisions is inefficient, making gases poor conductors.

Examiner tips

  • Use the word ‘free (delocalised) electrons’ for metals, ‘lattice vibrations’ for non‑metals, and ‘infrequent collisions’ for gases.
  • Show the contrast between electron transfer and phonon transfer.
  • Mention the distance between particles in gases as the reason for poor conduction.
  • Keep each point brief and use the exact terminology.

Common mistakes

  • Confusing electron transfer with lattice vibrations in metals.
  • Saying that gases conduct well because of collisions, without noting the infrequency.
  • Using vague terms like ‘fast’ or ‘slow’ without linking to electrons or phonons.

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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