# Iodine is a simple molecular covalent substance that exists as diatomic molecules, I₂. Explain why iodine is a solid at room temperature but has a much lower melting point than diamond, which is also a covalent substance.

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

## Mark scheme (4 marks)

1. Iodine has (weak) intermolecular forces between its I₂ molecules
2. Only a small amount of energy is needed to overcome these intermolecular forces, so the melting point is low
3. Diamond has a giant covalent structure with many strong covalent bonds throughout the structure
4. A large amount of energy is needed to break the many strong covalent bonds in diamond, giving it a very high melting point

## Key terms

- [simple molecular](https://www.gradenine.co.uk/glossary/simple-molecular)
- [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/iodine-is-a-simple-molecular-covalent-a408fe7a) · Published by Druglandscape Ltd.