# Chlorine, bromine and iodine are all elements in Group 7 of the periodic table. Describe how the reactivity of the Group 7 elements changes as you go down the group, and explain why this trend occurs in terms of atomic structure.

> WJEC A-Level Chemistry (Wales) — 2.2 Group 1, 2 and 7 · Describe and Explain · 5 marks

## Mark scheme (5 marks)

1. Reactivity decreases going down Group 7
2. Going down the group, the atoms have more electron shells
3. The outer shell is further from the nucleus, so the nucleus has less attraction for an incoming electron
4. Group 7 elements react by gaining one electron to form a negative ion (halide ion)
5. Because it is harder to attract an electron as you go down the group, each successive element is less reactive

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Chemistry (Wales)](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/chlorine-bromine-and-iodine-are-all-6a33d21b) · Published by Druglandscape Ltd.