# The periodic table arranges elements in order of increasing atomic number. Explain what is meant by the terms 'group' and 'period' in the periodic table, and describe how the number of electron shells and the number of electrons in the outer shell relate to an element's position in the periodic table.

> WJEC A-Level Chemistry (Wales) — 2.1 Periodic table · Explain · 5 marks

## Mark scheme (5 marks)

1. A group is a column of the periodic table
2. Elements in the same group have similar chemical properties
3. A period is a row of the periodic table
4. Elements in the same period have the same number of electron shells
5. Elements in the same group have the same number of electrons in their outer shell / outer energy level

## Key terms

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

## 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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/the-periodic-table-arranges-elements-in-62c5aa70) · Published by Druglandscape Ltd.