# Oxygen has an atomic number of 8 and a mass number of 16. State the number of protons, neutrons and electrons in one atom of oxygen, and explain why the overall charge of the atom is zero.

> WJEC GCSE Chemistry (Wales) — 2.1 Bonding, structure and properties · State · 4 marks

## Mark scheme (4 marks)

1. Number of protons = 8
2. Number of neutrons = 8 (mass number − atomic number = 16 − 8)
3. Number of electrons = 8
4. The number of (negatively charged) electrons equals the number of (positively charged) protons, so the charges cancel / balance out

## 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 WJEC GCSE Chemistry (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "State" 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/oxygen-has-an-atomic-number-of-834756e5) · Published by Druglandscape Ltd.