# Explain why elements in Group 7 of the periodic table become less reactive as you go down the group.

> Edexcel A-Level Chemistry (9CH0) — 1.2 Periodic table and trends · Explain · 5 marks

> Group 7 elements are known as the halogens. Fluorine is the most reactive halogen, and reactivity decreases going down the group from fluorine to astatine.

## Mark scheme (5 marks)

1. Halogens react by gaining one electron (to complete their outer shell / to form a negative ion / to achieve a full outer shell)
2. As you go down Group 7, the atoms get larger / have more electron shells
3. The outer shell / incoming electron is further from the (positive) nucleus
4. There is greater shielding / shielding by inner electrons increases going down the group
5. So the nucleus attracts the incoming electron less strongly / it is harder to gain an electron, making the element less reactive

## Key terms

- [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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