# Explain the difference between the mass number and the atomic number of an atom, and state what is meant by isotopes of the same element.

> Eduqas GCSE Physics — 9.1 Nuclear atom and isotopes · Explain · 4 marks

## Mark scheme (4 marks)

1. The atomic number is the number of protons in the nucleus
2. The mass number is the total number of protons and neutrons in the nucleus
3. Isotopes are atoms of the same element that have the same number of protons
4. Isotopes have different numbers of neutrons (so different mass numbers)

## Key terms

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

## Related

- [Revision notes for Eduqas GCSE Physics](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-the-difference-between-the-mass-d4d7a6cc) · Published by Druglandscape Ltd.