# Explain what is meant by the term 'isotopes' and describe how two isotopes of the same element are similar and how they differ in terms of their atomic structure.

> WJEC A-Level Physics (Wales) — 1.7 Particles and nuclear structure · Explain · 5 marks

## Mark scheme (5 marks)

1. Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons
2. The two isotopes have the same number of protons (accept: same atomic/proton number)
3. The two isotopes have different numbers of neutrons (accept: different mass numbers)
4. The two isotopes have the same number of electrons (accept: same electron arrangement / same electronic structure)
5. Because the number of electrons is the same, isotopes of the same element have the same chemical properties (accept: behave the same chemically / react in the same way)

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Physics (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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-what-is-meant-by-the-968c295e) · Published by Druglandscape Ltd.