# Fluorine, chlorine and bromine are all elements in Group 7 of the periodic table. When chlorine gas is bubbled through a solution of potassium bromide, a reaction takes place. Explain why this reaction occurs and predict whether fluorine would react in a similar way with potassium bromide solution, justifying your answer. Include reference to electron shells in your answer.

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

> Group 7 elements are also known as the halogens. Their reactivity changes as you move down the group.

## Mark scheme (5 marks)

1. Chlorine is more reactive than bromine (accept: chlorine is higher/above bromine in Group 7)
2. A more reactive halogen displaces a less reactive halogen from its salt solution (accept: chlorine displaces bromide ions from the solution)
3. As you go down Group 7, atoms have more electron shells / the outer electron shell is further from the nucleus
4. It is harder to gain an electron as you go down the group, so reactivity decreases going down Group 7 (accept: chlorine gains an electron more easily than bromine)
5. Fluorine would react with potassium bromide solution because fluorine is more reactive than chlorine / fluorine is above chlorine in Group 7 / fluorine has fewer electron shells so gains an electron most easily

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Chemistry (Wales)](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-and-bromine-are-all-b717d2c5) · Published by Druglandscape Ltd.