# Magnesium has three naturally occurring isotopes: magnesium-24, magnesium-25, and magnesium-26. The relative atomic mass of magnesium is 24.3. Explain what is meant by the term 'isotope' and explain why the relative atomic mass of magnesium is not a whole number.

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

## 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 three isotopes of magnesium exist in different amounts / different abundances.
3. The relative atomic mass is an average value that takes account of the abundance of the isotopes of the element.
4. Because the average is weighted by abundance, 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/magnesium-has-three-naturally-occurring-isotopes-0e6598f4) · Published by Druglandscape Ltd.