# Silicon has three naturally occurring isotopes: silicon-28, silicon-29, and silicon-30. The relative atomic mass of silicon is 28.1. Explain what is meant by the term 'isotope' and use the information given to explain why the relative atomic mass of silicon is not a whole number.

> Eduqas GCSE Chemistry — 2.4 Chemical analysis · 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. Relative atomic mass takes account of the abundance (proportion) of each isotope
3. Silicon-28 is the most abundant isotope, so the relative atomic mass is closest to 28
4. Because the heavier isotopes (silicon-29 and silicon-30) are also present, the average is pulled above 28, giving a non-whole number value of 28.1

## Key terms

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

## Related

- [Revision notes for Eduqas GCSE Chemistry](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/silicon-has-three-naturally-occurring-isotopes-022fad3e) · Published by Druglandscape Ltd.