Explain why simple molecular substances, such as chlorine, have low melting points.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Chlorine exists as simple molecules. It is a gas at room temperature and pressure.
Model answer (4 marks)
Chlorine molecules are held together by weak intermolecular forces (London dispersion forces). These forces are very weak, so only a small amount of energy is required to overcome them. Consequently, the melting point is low. The covalent bonds within each Cl₂ molecule remain intact during melting.
Examiner tips
- Use the word ‘intermolecular forces’ and specify London dispersion forces; mention they are weak.
- Explain that only a small amount of energy is needed to break them.
- State that covalent bonds stay intact – no breaking of intra‑molecular bonds.
Mark scheme (4 marks)
- Chlorine molecules are held together by intermolecular forces (between molecules)
- These intermolecular forces are weak
- Only a small amount of energy is needed to overcome / break these intermolecular forces
- The covalent bonds within the molecule are not broken during melting
Key terms in this question
Related
- All AQA GCSE Chemistry (8462) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →