# Methane is the simplest alkane. Describe what happens when methane reacts with chlorine in the presence of ultraviolet light, and explain why this type of reaction is described as substitution.

> Cambridge International IGCSE Chemistry (0620) — 11.4 Alkanes · Describe and Explain · 4 marks

## Mark scheme (4 marks)

1. Ultraviolet light is needed to initiate / start the reaction
2. A hydrogen atom in methane is replaced by a chlorine atom
3. Chloromethane (CH3Cl) is formed as an organic product
4. Substitution means an atom (or group) is replaced by another atom (or group), so a hydrogen atom is replaced rather than an addition across a bond occurring

## Key terms

- [alkane](https://www.gradenine.co.uk/glossary/alkane)
- [substitution](https://www.gradenine.co.uk/glossary/substitution)
- [ultraviolet light](https://www.gradenine.co.uk/glossary/ultraviolet-light)

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/methane-is-the-simplest-alkane-describe-49fea31c) · Published by Druglandscape Ltd.