# Explain how the atomic number and mass number of an atom can be used to determine the number of protons, neutrons and electrons in that atom. Use the example of an atom with atomic number 11 and mass number 23.

> Eduqas GCSE Chemistry — C1 Atomic structure and the periodic table · Explain · 4 marks

## Mark scheme (4 marks)

1. The atomic number equals the number of protons (in this case 11 protons)
2. In a neutral atom the number of electrons equals the number of protons (so 11 electrons)
3. The number of neutrons is found by subtracting the atomic number from the mass number
4. The number of neutrons in this atom is 12

## 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 Eduqas GCSE Chemistry](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-atomic-number-and-a4720ec4) · Published by Druglandscape Ltd.