# Chlorine has two naturally occurring isotopes: chlorine-35 and chlorine-37. Explain why these two isotopes have the same chemical properties but different relative atomic masses.

> Cambridge International IGCSE Chemistry (0620) — 2.3 Isotopes · Explain · 4 marks

## Mark scheme (4 marks)

1. Isotopes have the same number of protons / same atomic number / same number of electrons
2. Chemical properties are determined by the number of electrons / electron arrangement
3. Isotopes have different numbers of neutrons
4. Different numbers of neutrons give different masses / mass numbers, so relative atomic masses differ

## Key terms

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

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/chlorine-has-two-naturally-occurring-isotopes-cc8fbe04) · Published by Druglandscape Ltd.