# Chlorine, bromine and iodine are all elements in Group 7 of the periodic table. Explain why these three elements have similar chemical properties, and describe how their reactivity changes going down the group.

> Eduqas A-Level Chemistry — 2.2 Group 1, 2 and 7 · Explain · 5 marks

## Mark scheme (5 marks)

1. Elements in the same group have the same number of electrons in their outer shell
2. It is the outer shell electrons that determine chemical properties / reactivity
3. Reactivity decreases going down Group 7 (from chlorine to iodine)
4. Going down the group, atoms have more electron shells
5. The outer shell is further from the nucleus so it is harder to attract an additional electron, making the atom less reactive

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Chemistry](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-c6ce9977) · Published by Druglandscape Ltd.