# Fluorine, chlorine, bromine and iodine are all elements in Group 7 of the periodic table, known as the halogens. Explain how the reactivity of the halogens changes as you move down Group 7, linking this trend to changes in atomic structure.

> OCR A-Level Chemistry A (H432) — 3.1 The periodic table and periodicity · Explain · 5 marks

> The halogens are a group of non-metals that react with metals and hydrogen to form salts. Their physical and chemical properties show clear periodic trends.

## Mark scheme (5 marks)

1. Reactivity decreases as you go down Group 7
2. Each element in Group 7 needs to gain one electron to achieve a full outer shell
3. As you go down the group, the atoms have more electron shells / are larger
4. The outer shell is further from the nucleus as you go down the group, so the attraction between the nucleus and an incoming electron is weaker
5. Therefore, it becomes harder to gain an electron, so the element is less reactive

## Key terms

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

## Related

- [Revision notes for OCR A-Level Chemistry A (H432)](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/fluorine-chlorine-bromine-and-iodine-are-5c5bc27a) · Published by Druglandscape Ltd.