# Chlorine has two naturally occurring isotopes, chlorine-35 and chlorine-37. Explain what is meant by the term isotope and describe how these two isotopes of chlorine are similar and how they are different in terms of their subatomic particles.

> Eduqas A-Level Chemistry — 2.3 Transition metals (A-Level only) · Explain · 5 marks

## Mark scheme (5 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).
4. The two isotopes have different numbers of neutrons.
5. This means the two isotopes have different mass numbers (35 and 37), so chlorine-37 has a greater mass than chlorine-35.

## Key terms

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

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Source: [GradeNine](https://www.gradenine.co.uk/q/chlorine-has-two-naturally-occurring-isotopes-7393c103) · Published by Druglandscape Ltd.