# Copper has atomic number 29. One isotope of copper has mass number 63 and another has mass number 65. Explain why these two isotopes have the same chemical properties but different mass numbers.

> Pearson Edexcel International GCSE Chemistry (4CH1) — 1.3 Atomic structure · Explain · 4 marks

## Mark scheme (4 marks)

1. Both isotopes have the same number of protons (29) / same atomic number
2. Both isotopes have the same number of electrons (29) / same electron arrangement / same electronic structure
3. Chemical properties depend on the number / arrangement of electrons
4. The isotopes have different numbers of neutrons (copper-63 has 34 neutrons; copper-65 has 36 neutrons), giving different mass numbers

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel International GCSE Chemistry (4CH1)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/copper-has-atomic-number-29-one-d02097e2) · Published by Druglandscape Ltd.