# Astatine is a halogen found below iodine in Group 7. A student carries out displacement reactions using solutions of potassium fluoride, potassium chloride, potassium bromide and potassium iodide. The student adds astatine solution to each. Predict and explain the results the student would observe, and state which solution(s) would show a positive result.

> Edexcel A-Level Chemistry (9CH0) — 4.2 Group 7 halogens · Explain · 5 marks

> Astatine is a very rare halogen at the bottom of Group 7. Like the other halogens, it can take part in displacement reactions with halide salts.

## Mark scheme (5 marks)

1. Astatine is the least reactive halogen (in Group 7) / less reactive than fluorine, chlorine, bromine and iodine
2. A more reactive halogen displaces a less reactive halogen from its salt / displacement only occurs when the added halogen is more reactive than the halide in solution
3. Astatine will NOT displace fluoride, chloride, bromide or iodide ions / none of the four solutions will show a positive result / no colour change is observed in any solution
4. Reactivity of halogens decreases down Group 7 because the atoms get larger / the outer shell gets further from the nucleus (as you go down the group)
5. The ability to attract / gain an electron to form a halide ion decreases down Group 7, making astatine the least able to gain an electron and therefore least reactive

## Key terms

- [displacement](https://www.gradenine.co.uk/glossary/displacement)
- [halogen](https://www.gradenine.co.uk/glossary/halogen)
- [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/astatine-is-a-halogen-found-below-580bee58) · Published by Druglandscape Ltd.