# Define the term 'relative atomic mass' and explain why the relative atomic mass of chlorine is not a whole number.

> Cambridge International IGCSE Chemistry (0620) — 3.2 Relative masses of atoms and molecules · Define and Explain · 4 marks

## Mark scheme (4 marks)

1. Relative atomic mass is the average mass of one atom of an element
2. compared to 1/12 of the mass of one atom of carbon-12 (or compared to one atom of hydrogen / relative to the carbon-12 scale)
3. Chlorine exists as more than one isotope (chlorine-35 and chlorine-37)
4. The relative atomic mass is a weighted average of the masses of all naturally occurring isotopes (in their natural abundances), giving a non-whole-number value

## Key terms

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

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](https://www.gradenine.co.uk/learn)
- [How to answer "Define and 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/define-the-term-relative-atomic-mass-c23677aa) · Published by Druglandscape Ltd.