# Chlorine has two stable isotopes: chlorine-35 and chlorine-37. Describe what is meant by the term isotope and state how the two isotopes of chlorine are similar and how they are different in terms of their subatomic particles.

> Pearson Edexcel International GCSE Chemistry (4CH1) — 1.3 Atomic structure · Describe · 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 each)
3. Both isotopes have the same number of electrons (17 electrons each)
4. The two isotopes have different numbers of neutrons (chlorine-35 has 18 neutrons; chlorine-37 has 20 neutrons)

## Key terms

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

## Related

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Source: [GradeNine](https://www.gradenine.co.uk/q/chlorine-has-two-stable-isotopes-chlorine-35-1ad6cf97) · Published by Druglandscape Ltd.