The Development of the Atomic Model

This lesson covers the historical development of the atomic model as required by AQA GCSE Combined Science Trilogy (8464, Chemistry 4.1.1). You need to know how the model of the atom has changed over time as new experimental evidence was discovered. This is a very common exam topic — AQA frequently asks 6-mark questions on how and why the model has evolved.

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Why Do Scientific Models Change?

A model in science is a simplified representation used to explain observations. Models change when new experimental evidence is discovered that the existing model cannot explain. Each new model builds on the previous one and provides a better explanation of the behaviour of atoms.

Exam Tip (AQA 8464): When discussing the development of the atomic model, always link each change to the new evidence that caused it. Simply listing the models without explaining why they changed will lose you marks.

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Timeline of the Atomic Model

graph LR
    A["Dalton<br/>Early 1800s<br/>Solid sphere"] --> B["Thomson<br/>1897<br/>Plum pudding model"]
    B --> C["Rutherford<br/>1909<br/>Nuclear model"]
    C --> D["Bohr<br/>1913<br/>Electron shells"]
    D --> E["Chadwick<br/>1932<br/>Discovery of neutron"]