# Copper has two naturally occurring isotopes: copper-63 and copper-65. Explain why the relative atomic mass of copper is not a whole number.

> Eduqas GCSE Chemistry — 2.4 Chemical analysis · Explain · 4 marks

> The relative atomic mass of copper is 63.5.

## Mark scheme (4 marks)

1. Isotopes are atoms of the same element with the same number of protons but a different number of neutrons
2. The two isotopes have different masses / mass numbers (63 and 65)
3. Relative atomic mass is an average value that takes account of the abundance of each isotope
4. Because the average is taken across isotopes of different masses, the result is not a whole number

## Key terms

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

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Source: [GradeNine](https://www.gradenine.co.uk/q/copper-has-two-naturally-occurring-isotopes-013f0743) · Published by Druglandscape Ltd.