Explain why metals have high melting points and are malleable (can be bent and shaped without breaking).
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. The strong electrostatic attraction between the ions and the electron cloud gives the lattice a high cohesive energy, so a large amount of energy is required to break the bonds and melt the metal. When a metal is deformed, layers of ions can slide past one another because the delocalised electrons remain free to move with the ions, so the metallic bonds are not broken and the metal is malleable.
Examiner tips
- Mention the ion lattice and delocalised electrons first.
- Explain that strong ion–electron attraction gives high melting point.
- State that sliding layers is possible because electrons move with ions.
- Use the exact terms "electrostatic forces" and "malleable".
Common mistakes
- Confusing metallic bonding with covalent or ionic bonds.
- Failing to mention the delocalised electrons as the reason for malleability.
- Using vague terms like "strong bonds" without specifying electrostatic attraction.
Mark scheme (4 marks)
- Metals consist of a lattice of positive ions
- There are strong electrostatic forces of attraction between the positive ions and the sea of delocalised electrons
- A large amount of energy is needed to overcome these strong forces, giving a high melting point
- Layers of positive ions can slide over one another without breaking the metallic bonding, because the delocalised electrons move with the ions
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 →