# Fluorine, chlorine, bromine and iodine are all members of Group 7. Describe the trend in physical appearance of the halogens from fluorine to iodine at room temperature and pressure, and explain what this tells us about the reactivity of the halogens down the group.

> AQA A-Level Chemistry (7405) — 3.2.3 Group 7(17), the halogens · Describe · 5 marks

> At room temperature and pressure, fluorine is a pale yellow gas, chlorine is a yellow-green gas, bromine is a red-brown liquid, and iodine is a grey-black solid.

## Mark scheme (5 marks)

1. The halogens change from gas to liquid to solid going down the group (fluorine and chlorine are gases, bromine is a liquid, iodine is a solid)
2. The colour darkens / becomes deeper going down the group (from pale yellow to grey-black)
3. Reactivity decreases going down Group 7
4. Because atomic radius increases down the group, so the outer shell is further from the nucleus
5. So it is harder to attract an extra electron to complete the outer shell / gain an electron, making the halogen a weaker oxidising agent

## Key terms

- [halogen](https://www.gradenine.co.uk/glossary/halogen)
- [reactivity](https://www.gradenine.co.uk/glossary/reactivity)

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/fluorine-chlorine-bromine-and-iodine-are-3b6cb39f) · Published by Druglandscape Ltd.