# Explain why simple molecular covalent substances, such as water and carbon dioxide, have low melting points, whereas giant covalent structures, such as diamond, have very high melting points.

> Pearson Edexcel International GCSE Chemistry (4CH1) — 1.7 Covalent substances · Explain · 4 marks

## Mark scheme (4 marks)

1. Simple molecular substances have weak intermolecular forces between molecules
2. Little energy is needed to overcome these weak intermolecular forces, so the melting point is low
3. Giant covalent structures contain many strong covalent bonds throughout the structure
4. A large amount of energy is needed to break these strong covalent bonds, so the melting point is very high

## Key terms

- [simple molecular covalent substance](https://www.gradenine.co.uk/glossary/simple-molecular-covalent-substance)
- [giant covalent structure](https://www.gradenine.co.uk/glossary/giant-covalent-structure)
- [melting point](https://www.gradenine.co.uk/glossary/melting-point)

## Related

- [Revision notes for Pearson Edexcel International GCSE Chemistry (4CH1)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-simple-molecular-covalent-substances-3b66bf42) · Published by Druglandscape Ltd.