# Two atoms of the same element have different nucleon numbers. State what is meant by the term 'nucleon number' and explain why two atoms of the same element can have different nucleon numbers.

> Cambridge International IGCSE Physics (0625) — 5.1 The nuclear model of the atom · State and Explain · 4 marks

## Mark scheme (4 marks)

1. Nucleon number is the total number of protons and neutrons in an atom / nucleus.
2. Atoms of the same element have the same number of protons / the same proton number.
3. The two atoms have different numbers of neutrons.
4. These atoms are called isotopes (of the same element).

## Key terms

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

## Related

- [Revision notes for Cambridge International IGCSE Physics (0625)](https://www.gradenine.co.uk/learn)
- [How to answer "State and 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/two-atoms-of-the-same-element-95578511) · Published by Druglandscape Ltd.