# A neutral atom of sodium has a proton number of 11 and a nucleon number of 23. State the number of protons, neutrons, and electrons in this atom, and explain how the atom would change if it lost one electron.

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

## Mark scheme (4 marks)

1. 11 protons
2. 12 neutrons (nucleon number minus proton number = 23 − 11)
3. 11 electrons (equal to number of protons in a neutral atom)
4. Losing one electron would form a positive ion / the atom would become a positive ion because there would be more protons than electrons

## Key terms

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

## 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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-neutral-atom-of-sodium-has-c68872f1) · Published by Druglandscape Ltd.