Explain why metals can be drawn into wires (are ductile) without breaking, and why metals generally have high melting points.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Metals are made of a lattice of positive ions surrounded by a sea of delocalised electrons. When a force is applied the layers of ions can slide over one another, so the metal can be stretched into a wire without breaking – this is ductility. The delocalised electrons give rise to strong electrostatic attraction (metallic bonds) between the positive ions. A large amount of energy is required to overcome these strong attractions, so metals have high melting points.
Examiner tips
- Use the term ‘delocalised electrons’ and ‘metallic bonds’ to show understanding of the structure.
- Explain that ductility comes from ion layers sliding, not from the electrons themselves.
- Show that high melting points result from the energy needed to break the metallic bonds.
- Keep the answer concise – 4 marks can be earned with two short sentences.
Common mistakes
- Confusing ductility with malleability or saying the electrons themselves slide.
- Omitting the sea of delocalised electrons or the lattice of ions.
- Claiming high melting points are due to covalent bonds or crystal lattice only, without mentioning metallic bonds.
Mark scheme (4 marks)
- Metals consist of a lattice of positive ions surrounded by a sea of delocalised electrons
- Layers of ions can slide over one another when a force is applied, so the metal can be stretched into a wire without breaking
- Strong electrostatic attraction / metallic bonds exist between the positive ions and the delocalised electrons
- A large amount of energy is needed to overcome these strong attractions, so metals have high melting points
Key terms in this question
Related
- All Cambridge International IGCSE Chemistry (0620) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →