# Hydrogen has three isotopes: protium (hydrogen-1), deuterium (hydrogen-2), and tritium (hydrogen-3). Explain why all three isotopes of hydrogen have identical chemical properties but different physical properties such as density.

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

## Mark scheme (4 marks)

1. All three isotopes have the same number of protons / the same atomic number (1 proton each)
2. Identical chemical properties because all three have the same number of electrons / same electronic configuration
3. The isotopes have different numbers of neutrons (protium has 0, deuterium has 1, tritium has 2)
4. Different numbers of neutrons give different masses / different relative atomic masses, leading to different physical properties such as density

## Key terms

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

## 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/hydrogen-has-three-isotopes-protium-hydrogen-1-2487bce0) · Published by Druglandscape Ltd.