Steel cables are used to suspend large bridges. Suggest why the metallic structure of steel makes it suitable for this purpose. Give two reasons.

Cambridge International IGCSE Chemistry (0620) — 9.1 Properties of metals · Suggest · 4 marks · View as Markdown

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

Steel cables in suspension bridges must support enormous loads without snapping, and must be able to flex slightly as vehicles cross.

Model answer (4 marks)

Steel has a high tensile strength, so it can support the enormous loads of a suspension bridge without breaking.
The metallic structure of steel gives it ductility; the layers of metal ions can slide over one another when a force is applied, allowing the cable to flex slightly as vehicles cross without cracking.

Examiner tips

  • Use the word ‘tensile strength’ for the first reason, and ‘ductility’ or ‘malleability’ for the second. Include the idea of sliding layers or delocalised electrons to show understanding of metallic bonding. Keep the answer concise and directly linked to the question.

Common mistakes

  • Writing ‘hardness’ instead of tensile strength; ‘hardness’ is not relevant to load‑bearing ability. Forgetting to mention the sliding of metal layers or the delocalised electrons, which shows the metallic bond explanation. Using vague terms like ‘strong’ or ‘flexible’ without the specific terminology examiners expect.

Mark scheme (4 marks)

  1. Steel has high tensile strength / is strong, so it can support heavy loads without breaking
  2. Metallic bonds are strong / metal ions are held together by a sea of delocalised electrons, so the structure does not easily break
  3. Steel is malleable / ductile, so the cable can flex / bend without snapping
  4. Layers of metal ions can slide over one another when a force is applied, so the structure does not crack

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