Poly(ethene) is a simple molecular covalent substance used to make plastic bags. It does not conduct electricity and has a relatively low melting point. Explain why poly(ethene) does not conduct electricity and why it has a low melting point.

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

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

Poly(ethene) is a simple molecular covalent substance. It is used to make plastic bags and food packaging because it is flexible and has a low melting point.

Model answer (4 marks)

Poly(ethene) does not conduct electricity because it has no charged particles that are free to move.
Poly(ethene) has a low melting point because the molecules are held together only by weak van der Waals forces.
Only a small amount of energy is required to overcome these weak forces.
The strong covalent bonds within each polymer chain are not broken on melting.

Examiner tips

  • Use the exact phrase ‘no charged particles that are free to move’ for the conductivity point.
  • Mention ‘weak van der Waals forces’ for the melting point explanation.
  • Show that only a small amount of energy is needed and that covalent bonds remain intact.”]
  • common_mistakes

Mark scheme (4 marks)

  1. Poly(ethene) does not conduct electricity because it has no charged particles that are free to move
  2. Poly(ethene) has a low melting point because it has weak intermolecular forces between molecules
  3. Only a small amount of energy is needed to overcome the weak intermolecular forces
  4. The strong covalent bonds within the molecules are NOT broken on melting

Key terms in this question

simple molecular covalent substance

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