Explain why sodium chloride has a high melting point.

OCR GCSE Chemistry A: Gateway Science (J248) — C2.2 Bonding · Explain · 4 marks · View as Markdown

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

Sodium chloride is an ionic compound used to grit roads in winter. Despite being exposed to very cold temperatures, large quantities of heat energy are needed to melt it.

Model answer (4 marks)

Sodium chloride consists of
1. positively charged Na⁺ ions and negatively charged Cl⁻ ions.
2. These ions are held together by strong electrostatic forces of attraction.
3. A large amount of energy is required to overcome these forces and break the ionic lattice apart.
4. Consequently, a high temperature is needed to melt sodium chloride.

Examiner tips

Use the exact terms "oppositely charged ions", "electrostatic forces of attraction", "break the forces apart", "high melting point".
Show the logical sequence: composition → forces → energy required → result.
Keep the answer concise – 4 points only, no extra words.

Common mistakes

Using vague terms like "strong bonds" instead of "electrostatic forces".
Omitting the step that the energy must overcome the ionic lattice.
Failing to mention that the ions are oppositely charged.

Mark scheme (4 marks)

Sodium chloride is made up of oppositely charged ions / contains positive sodium ions and negative chloride ions
The ions are held together by strong electrostatic forces (of attraction)
A large amount of energy is needed to overcome these forces / to break these forces apart
Therefore the melting point is high / a high temperature is required to melt sodium chloride

Key terms in this question

melting point