# Chlorine has two main isotopes: chlorine-35 and chlorine-37. Explain what is meant by the term isotope and describe how the atoms of these two isotopes of chlorine are similar and how they are different.

> WJEC GCSE Chemistry (Wales) — 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. Both isotopes have the same number of protons (17 protons)
3. Both isotopes have the same number of electrons (17 electrons) / same electronic structure / same chemical properties
4. The two isotopes have different numbers of neutrons / chlorine-35 has 18 neutrons and chlorine-37 has 20 neutrons / different mass numbers

## Key terms

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

## Related

- [Revision notes for WJEC GCSE Chemistry (Wales)](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-main-isotopes-chlorine-35-29cff89f) · Published by Druglandscape Ltd.