Explain why iodine has a low melting point and does not conduct electricity.

Edexcel GCSE Chemistry (1CH0) — 1.7 Types of substance · Explain · 4 marks · View as Markdown

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

Iodine is a non-metallic element that exists as a dark grey solid at room temperature. It is used as an antiseptic and in chemical tests.

Model answer (4 marks)

Iodine is a simple molecular substance made up of I₂ molecules.
The only forces between the molecules are weak London dispersion forces.
Because these forces are weak, only a small amount of energy is required to overcome them, so iodine has a low melting point.
Iodine does not conduct electricity because it has no free electrons or ions to carry charge.

Examiner tips

  • Use the word "molecular" to show understanding of the substance type. Explain that London forces are weak. Link weak forces to low melting point. State that lack of free electrons/ions means no conductivity.

Common mistakes

  • Confusing iodine with a metallic element. Forgetting to mention London dispersion forces. Saying iodine conducts electricity because of covalent bonds.

Mark scheme (4 marks)

  1. Iodine is a simple molecular substance made up of I₂ molecules
  2. The intermolecular forces (between molecules) are weak
  3. Only a small amount of energy is needed to overcome these weak intermolecular forces, so the melting point is low
  4. Iodine does not conduct electricity because it has no free electrons or ions to carry charge

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