# Boron has two isotopes, boron-10 and boron-11. The relative atomic mass of boron is 10.8. Explain what the term isotope means and explain why the relative atomic mass of boron is not a whole number.

> AQA GCSE Chemistry (8462) — 4.1.1 A simple model of the atom, symbols, relative atomic mass, electronic charge and isotopes · 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. Boron-10 and boron-11 have different abundances (they are not present in equal amounts)
3. Relative atomic mass is an average value that takes account of the abundance of the isotopes
4. Because the average is weighted towards boron-11 (the more abundant isotope), the result is not a whole number

## 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 AQA GCSE Chemistry (8462)](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/boron-has-two-isotopes-boron-10-and-bbde7c63) · Published by Druglandscape Ltd.