# Chlorine has two isotopes: chlorine-35 and chlorine-37. Explain what is meant by the term isotope and explain why the relative atomic mass of chlorine is not a whole number.

> Eduqas GCSE Chemistry — 2.5 The production of important chemicals · 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 relative atomic mass is an average value that takes account of the abundance of the isotopes
3. Chlorine-35 and chlorine-37 exist in different proportions / abundances, so the average is not a whole number
4. The average value (approximately 35.5) falls between the two mass numbers 35 and 37, so it cannot be 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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- [Revision notes for Eduqas GCSE Chemistry](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/chlorine-has-two-isotopes-chlorine-35-and-9acf38a0) · Published by Druglandscape Ltd.