# Chlorine, bromine and iodine are all halogens found in Group 7 of the periodic table. Explain why the halogens become less reactive as you go down Group 7.

> Edexcel A-Level Chemistry (9CH0) — Topic 2 Inorganic chemistry and the Periodic Table · Explain · 5 marks

> Halogens react with metals and non-metals by gaining one electron to form a negative ion. The reactivity of halogens decreases going down the group.

## Mark scheme (5 marks)

1. Atoms gain one electron (to complete their outer shell / form a full outer shell)
2. Going down the group, atoms have more electron shells / the outer shell is further from the nucleus
3. There is greater shielding of the nucleus by inner electron shells going down the group
4. The attraction between the nucleus and the incoming electron is weaker (going down the group)
5. So it is harder / less easy to gain an electron, making the halogen less reactive going down the group

## Key terms

- [halogens](https://www.gradenine.co.uk/glossary/halogens)
- [Group 7](https://www.gradenine.co.uk/glossary/group-7)

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/chlorine-bromine-and-iodine-are-all-ac1d29db) · Published by Druglandscape Ltd.