# A neutral atom of chlorine-35 becomes a negative ion. Explain what happens to the subatomic particles in the atom to form a negative ion, and state how the mass number and atomic number are each affected.

> AQA GCSE Physics (8463) — 4.4.1 Atoms and isotopes · Explain · 4 marks

> Chlorine-35 has a mass number of 35 and an atomic number of 17.

## Mark scheme (4 marks)

1. The atom gains one or more electrons
2. There are now more electrons than protons, giving a resultant negative charge
3. The atomic number (number of protons) is unchanged / stays at 17
4. The mass number is unchanged / stays at 35

## Key terms

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

## Related

- [Revision notes for AQA GCSE Physics (8463)](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/a-neutral-atom-of-chlorine-35-becomes-e80b5b53) · Published by Druglandscape Ltd.