# An atom of carbon-12 and an atom of carbon-14 are both described as isotopes of carbon. State what is meant by the term isotope, and explain why carbon-12 and carbon-14 have different mass numbers despite being the same element.

> Eduqas GCSE Physics — 9.1 Nuclear atom and isotopes · State and Explain · 4 marks

## Mark scheme (4 marks)

1. Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons
2. The mass number is the total number of protons and neutrons (nucleons) in the nucleus
3. Carbon-12 has 6 neutrons whereas carbon-14 has 8 neutrons (both have 6 protons)
4. Because carbon-14 has more neutrons, the total number of protons plus neutrons is greater, giving it a higher mass number

## Key terms

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

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- [Revision notes for Eduqas GCSE Physics](https://www.gradenine.co.uk/learn)
- [How to answer "State and Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/an-atom-of-carbon-12-and-an-bfe47aa9) · Published by Druglandscape Ltd.