# Fluorine, chlorine, bromine, and iodine are all non-metals found in Group 7 of the periodic table. As you move down Group 7, the elements change from gases to liquids to solids at room temperature, and their reactivity decreases. Explain, in terms of atomic structure and electron arrangement, why the reactivity of the Group 7 elements decreases going down the group.

> OCR A-Level Chemistry B: Salters (H433) — 3.1 The periodic table and periodicity · Explain · 5 marks

> Group 7 elements react by gaining one electron to form a negatively charged ion with a stable electron arrangement. Fluorine is the most reactive halogen, and reactivity decreases going down the group from fluorine to iodine.

## Mark scheme (5 marks)

1. Going down Group 7, each successive element has one more electron shell (energy level)
2. The outer shell (where the electron is gained) is further from the nucleus going down the group
3. There is greater shielding of the nucleus by inner electron shells going down the group
4. The attractive force of the nucleus on an incoming electron decreases going down the group
5. Therefore the atom finds it harder to gain an electron, so reactivity decreases going down the group

## Key terms

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

## Related

- [Revision notes for OCR A-Level Chemistry B: Salters (H433)](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-bromine-and-iodine-are-7cabcc0c) · Published by Druglandscape Ltd.