# Explain how the number of protons, neutrons and electrons in an atom determines its atomic number, mass number and overall charge.

> Cambridge International IGCSE Chemistry (0620) — 2.2 Atomic structure and the periodic table · Explain · 4 marks

> An atom of an element has an atomic number of 11 and a mass number of 23.

## Mark scheme (4 marks)

1. The atomic number equals the number of protons (in the nucleus)
2. The mass number equals the total number of protons plus neutrons
3. The number of neutrons is 12 (mass number minus atomic number / 23 − 11)
4. An atom has no overall charge because the number of protons equals the number of electrons (both 11 in this atom)

## Key terms

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

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](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-how-the-number-of-protons-15acae99) · Published by Druglandscape Ltd.