# Elements in the periodic table are arranged in periods and groups. Explain what the period number and the group number of an element tell you about the structure of its atoms.

> Eduqas GCSE Chemistry — C1 Atomic structure and the periodic table · Explain · 4 marks

## Mark scheme (4 marks)

1. The period number tells you the number of electron shells (energy levels) in the atom
2. The group number tells you the number of electrons in the outer shell (outermost energy level)
3. Correct application: a named example linking period to number of shells OR group to outer electrons (e.g. sodium is in period 3 so it has 3 shells; sodium is in group 1 so it has 1 electron in its outer shell)
4. Elements in the same group have similar chemical properties because they have the same number of outer shell electrons

## Key terms

- [period](https://www.gradenine.co.uk/glossary/period)
- [group](https://www.gradenine.co.uk/glossary/group)

## Related

- [Revision notes for Eduqas GCSE 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/elements-in-the-periodic-table-are-efee9899) · Published by Druglandscape Ltd.