# Explain why scientists changed the plum pudding model of the atom after the results of the alpha particle scattering experiment were published.

> AQA A-Level Chemistry (7405) — 3.1.1 Atomic structure · Explain · 5 marks

> In the early 1900s, Geiger and Marsden fired positively charged alpha particles at a thin sheet of gold foil. Most alpha particles passed straight through, but a small number were deflected at large angles, and a very small number bounced almost straight back.

## Mark scheme (5 marks)

1. In the plum pudding model, positive charge is spread evenly throughout the atom, so large deflections of alpha particles were not expected
2. Most alpha particles passing straight through shows that most of the atom is empty space
3. Some alpha particles were deflected at large angles / bounced back, showing a small, dense, positively charged nucleus exists
4. Only a very small proportion of alpha particles were deflected/bounced back, showing the nucleus is very small compared to the whole atom
5. The evidence contradicted the plum pudding model, so scientists revised it to produce the nuclear model in which electrons orbit a central nucleus

## Key terms

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

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](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-scientists-changed-the-plum-b513bd43) · Published by Druglandscape Ltd.