Explain why poly(ethene) has a low melting point and does not conduct electricity.

AQA A-Level Chemistry (7405) — 3.1.3 Bonding · Explain · 5 marks · View as Markdown

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

Poly(ethene) is a polymer used to make plastic bags and bottles. It is formed from many ethene monomers joined together into long chains.

Model answer (5 marks)

Poly(ethene) consists of long covalent chain molecules (polymers). The chains are held together only by weak van der Waals forces, so only a small amount of energy is required to overcome these forces and separate the chains. Consequently the melting point is low. In addition, poly(ethene) has no free electrons or ions, so it cannot carry charge and therefore does not conduct electricity.

Examiner tips

  • Use the word ‘only’ to emphasise weak forces and low energy needed.
  • Mention both van der Waals forces and lack of charge carriers.
  • Keep the answer concise – one sentence per point.
  • Use UK spelling (e.g. ‘covalent’).

Common mistakes

  • Confusing covalent bonds with ionic bonds; students may say the polymer is ionic.
  • Failing to mention the lack of free electrons/ions for conductivity.
  • Over‑explaining the polymer structure beyond the required points.

Mark scheme (5 marks)

  1. Poly(ethene) consists of long covalent chain molecules (polymers)
  2. There are weak intermolecular forces between the polymer chains
  3. Only a small amount of energy is needed to overcome these intermolecular forces
  4. Therefore the melting point is low / the chains separate at low temperature
  5. There are no free electrons or ions to carry charge, so poly(ethene) does not conduct electricity

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