# Explain why the nuclear model of the atom replaced the plum pudding model.

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

> Early scientists believed atoms were solid spheres of positive charge with electrons embedded throughout. Later experiments led to a new model being accepted by the scientific community.

## Mark scheme (5 marks)

1. In the plum pudding model, alpha particles were expected to pass straight through (with little or no deflection)
2. In the alpha particle scattering experiment, most alpha particles did pass straight through
3. A small number of alpha particles were deflected through large angles / some were deflected back
4. Large deflections could not be explained by the plum pudding model (so the model had to be changed)
5. The nuclear model proposed a small, dense, positively charged nucleus at the centre of the atom, which explains why some alpha particles were deflected through large angles

## Key terms

- [plum pudding model](https://www.gradenine.co.uk/glossary/plum-pudding-model)
- [nuclear model](https://www.gradenine.co.uk/glossary/nuclear-model)

## Related

- [Revision notes for AQA A-Level Physics (7408)](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/explain-why-the-nuclear-model-of-58342cd8) · Published by Druglandscape Ltd.