# Lithium, sodium and potassium are all in Group 1 of the periodic table. Explain why these three elements have similar chemical properties, and why their properties differ from the elements in Period 2 of the periodic table.

> Eduqas A-Level Chemistry — 2.1 Periodic table · Explain · 5 marks

> Lithium has atomic number 3, sodium has atomic number 11, and potassium has atomic number 19. All three are found in Group 1 of the periodic table.

## Mark scheme (5 marks)

1. Elements in the same group have the same number of outer electrons / electrons in the outermost shell
2. It is the number of outer electrons that determines chemical properties / reactivity
3. Elements in the same group have similar chemical properties (accept: react in a similar way)
4. Elements in the same period have the same number of electron shells
5. Elements in Period 2 have different numbers of outer electrons (from lithium, sodium and potassium), so they have different chemical properties

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level 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/lithium-sodium-and-potassium-are-all-38e80d22) · Published by Druglandscape Ltd.