# Describe how scientists' understanding of atomic structure developed from Dalton's model to the nuclear model. In your answer, refer to the key experiments and discoveries that led to changes in the model.

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

## Mark scheme (5 marks)

1. Dalton proposed that atoms were solid, indivisible spheres (or 'billiard ball' model)
2. Thomson discovered the electron (through cathode ray experiments), showing atoms contain smaller, negatively charged particles
3. Thomson proposed the plum pudding model, in which electrons are embedded in a ball of positive charge
4. Rutherford's alpha particle scattering experiment fired alpha particles at thin gold foil and found that most passed straight through
5. A small number of alpha particles were deflected at large angles (or bounced back), leading to the conclusion that the atom has a small, dense, positively charged nucleus

## Key terms

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

## Related

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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-how-scientists-understanding-of-atomic-ec7bc24a) · Published by Druglandscape Ltd.