Simple molecules such as water (H₂O) and chlorine (Cl₂) have low boiling points, yet they contain strong covalent bonds. Explain why simple molecules have low boiling points, and explain why simple molecules cannot conduct electricity.

Eduqas GCSE Chemistry — C2 Bonding, structure and properties · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Simple molecules have weak intermolecular forces between molecules
It is the intermolecular forces (not the covalent bonds) that are broken during boiling
Simple molecules do not have an overall electric charge / no charged particles
There are no free / mobile charged particles to carry electrical charge / current

Examiner tips

  • Use the exact wording from the mark scheme – e.g. "weak intermolecular forces" and "no free / mobile charged particles"
  • Explain that covalent bonds are internal to the molecule, not responsible for boiling point
  • Show the link between lack of charge and inability to conduct electricity
  • Keep the answer concise – 4 points, one sentence each

Common mistakes

  • Confusing covalent bonds with intermolecular forces as the reason for low boiling points
  • Mentioning ionisation or dissociation of the molecule
  • Claiming that the molecules have charges or that electrons are free to move

Mark scheme (4 marks)

  1. Simple molecules have weak intermolecular forces between molecules
  2. It is the intermolecular forces (not the covalent bonds) that are broken during boiling
  3. Simple molecules do not have an overall electric charge / no charged particles
  4. There are no free / mobile charged particles to carry electrical charge / current

Key terms in this question

simple molecules · covalent bond

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