Explain why sodium chloride has a high melting point.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Sodium chloride is an ionic compound formed from sodium ions and chloride ions arranged in a giant ionic lattice.
Model answer (4 marks)
Sodium chloride has a giant ionic lattice structure.
The lattice is held together by strong electrostatic forces of attraction between the Na⁺ and Cl⁻ ions.
A large amount of energy is required to overcome these forces and break the attractions.
Because the forces act in all directions throughout the lattice, a very large amount of energy is needed overall to melt the compound.
The lattice is held together by strong electrostatic forces of attraction between the Na⁺ and Cl⁻ ions.
A large amount of energy is required to overcome these forces and break the attractions.
Because the forces act in all directions throughout the lattice, a very large amount of energy is needed overall to melt the compound.
Examiner tips
- Use the word "lattice" and "electrostatic forces" to show understanding of structure. Show that the forces act in all directions to justify the high energy requirement. Mention that melting involves breaking these forces, not just a single bond.
Common mistakes
- Confusing ionic with covalent bonding. Failing to mention the lattice structure or the directionality of forces. Using vague terms like "strong bonds" without specifying electrostatic attraction.
Mark scheme (4 marks)
- Sodium chloride has a giant ionic lattice structure
- There are strong electrostatic forces of attraction between oppositely charged ions
- A large amount of energy is required to overcome these forces / break these attractions
- These forces act in all directions throughout the lattice (so a very large amount of energy is needed overall)
Key terms in this question
Related
- All Edexcel GCSE Chemistry (1CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →