# Explain how scientists' model of the atom changed from the ancient Greek idea of the atom to the nuclear model, describing the key developments in order.

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

## Mark scheme (5 marks)

1. Ancient Greeks / early scientists believed the atom was the smallest possible particle (indivisible / could not be broken down further)
2. Discovery of the electron led to the plum pudding model, in which the atom was a ball of positive charge with electrons embedded in it
3. Alpha particle scattering experiment showed that most alpha particles passed straight through, suggesting the atom is mostly empty space
4. Some alpha particles were deflected by large angles / a small number bounced back, showing there is a small, dense, positively charged nucleus at the centre
5. The nuclear model replaced the plum pudding model because the plum pudding model could not explain the large-angle deflections / electrons were found to orbit the nucleus rather than be embedded in positive charge

## Key terms

- [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-how-scientists-model-of-the-46f80d80) · Published by Druglandscape Ltd.