AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Before the discovery of the electron, atoms were thought to be tiny…
Full specification wording
The development of the model of the atom (common content with physics): Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided.
This statement describes the earliest scientific model of the atom, often linked to John Dalton in the early 1800s.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 2 of 14
- 2 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
This statement describes the earliest scientific model of the atom, often linked to John Dalton in the early 1800s. Atoms were imagined as solid, indivisible particles, like minute billiard balls. The model explained why chemical reactions conserve mass and why compounds have fixed composition, because atoms simply rearrange without splitting. It did not include any internal structure, so it could not explain electrical effects or radioactivity. The word atom comes from the Greek word meaning indivisible, which reflects this idea. Later evidence from cathode rays showed that atoms contain smaller, negatively charged particles, so the model had to be replaced. Understanding this starting point helps you see science as a sequence of models revised when new evidence appears.
What earns the marks
- State that atoms were modelled as solid, indivisible spheres before electrons were discovered.
- Explain that this model treated the atom as a single particle with no internal structure.
- Link the model to its success in explaining conservation of mass in chemical reactions.
- Recognise that the model was replaced when evidence for subatomic particles was obtained.
- Use the historical context of Dalton's atomic theory to date the model.
Common mistakes and how to put them right
Thinking the solid sphere model included a nucleus.
Put it right by stating it had no internal parts at all.
Believing atoms really are indivisible today.
Put it right by noting that atoms contain protons, neutrons and electrons.
Confusing the solid sphere model with the plum pudding model.
Put it right by remembering the plum pudding model came after the electron was discovered.
Exam tips
- Use the phrase indivisible sphere when describing the early model, as it matches the specification wording.
- Contrast the model with later models in one sentence to show progression of scientific ideas.
- If asked why the model changed, refer to new experimental evidence rather than opinion.
Try the lesson
The start of the The development of the model of the atom (common content with physics): Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided. lesson, made from checked teaching notes for this specification point.
Have a go first
Before the discovery of the electron, how were atoms described?
Listen
This statement describes the earliest scientific model of the atom, often linked to John Dalton in the early 1800s. Atoms were imagined as solid, indivisible particles, like minute billiard balls. The model explained why chemical reactions conserve mass and why compounds have fixed composition, because atoms simply rearrange without splitting. It did not include any internal structure, so it could not explain electrical effects or radioactivity. The word atom comes from the Greek word meaning indivisible, which reflects this idea. Later evidence from cathode rays showed that atoms contain smaller, negatively charged particles, so the model had to be replaced. Understanding this starting point helps you see science as a sequence of models revised when new evidence appears. A strong answer earns marks for these points. State that atoms were modelled as solid, indivisible spheres before electrons were discovered. Explain that this model treated the atom as a single particle with no internal structure. Link the model to its success in explaining conservation of mass in chemical reactions. Recognise that the model was replaced when evidence for subatomic particles was obtained. A common slip: Thinking the solid sphere model included a nucleus. Instead, stating it had no internal parts at all. Exam tip: Use the phrase indivisible sphere when describing the early model, as it matches the specification wording.
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Key words
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Indivisible particles
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Evidence-based model change
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See every definition
- Indivisible particles
- Tiny spheres that could not be divided, which is how atoms were thought of before the discovery of the electron.
- Evidence-based model change
- Science is a sequence of models revised when new evidence appears, such as cathode rays showing smaller, negatively charged particles inside atoms.
Label the diagram
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1Box 1
2Box 2
3Box 3
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