# Describe the evidence from the alpha particle scattering experiment that led scientists to conclude that an atom has a small, dense, positively charged nucleus.

> AQA A-Level Physics (7408) — 3.2.1 Particles · Describe · 5 marks

> Before the alpha particle scattering experiment, scientists used the plum pudding model to describe atomic structure. In this model, the atom was a sphere of positive charge with negative electrons embedded throughout.

## Mark scheme (5 marks)

1. Most alpha particles passed straight through the gold foil (with little or no deflection)
2. This shows that the atom is mostly empty space
3. A small number of alpha particles were deflected through large angles / back towards the source
4. This shows the nucleus is small (because so few particles were deflected)
5. The large deflections show the nucleus is positively charged (because it repels the positively charged alpha particles) AND dense / contains most of the mass of the atom

## Key terms

- [alpha particle scattering experiment](https://www.gradenine.co.uk/glossary/alpha-particle-scattering-experiment)
- [nucleus](https://www.gradenine.co.uk/glossary/nucleus)

## Related

- [Revision notes for AQA A-Level Physics (7408)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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/describe-the-evidence-from-the-alpha-695cd313) · Published by Druglandscape Ltd.