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The development of the model of the atom - Teacher Slides.pptx
The lesson slides with the teacher's notes on each slide, and every question and mark scheme built in. Built from the lesson script on 30 September 2026.
AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
The development of the model of the atom
Atomic structure
Lesson 3 of 10
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Warm-up
Atomic structure
Lesson 3 of 10
Answer each one, then check.
1
Who discovered the electron?
2
What is a scientific model?
3
What is an alpha particle?
4
What is evidence?
5
Who discovered the neutron?
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Warm-up - Answers
Atomic structure
Lesson 3 of 10
1
Who discovered the electron?
J. J. Thomson
2
What is a scientific model?
A simplified representation used to explain observations
3
What is an alpha particle?
Two protons and two neutrons (a helium nucleus)
4
What is evidence?
Results from experiments that support or reject an idea
5
Who discovered the neutron?
James Chadwick
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Learning Objectives
Atomic structure
Lesson 3 of 10
1
Describe how the atomic model has changed over time.
2
Describe the plum pudding model and the nuclear model.
3
Explain why the alpha particle scattering experiment led to the nuclear model.
4
Describe the contributions of Bohr, the discovery of the proton and Chadwick's neutron.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Atomic structure
Lesson 3 of 10
CHANGING MODELS
New experimental evidence may lead to a scientific model being changed or replaced.
The atom has been thought of as a solid sphere, a plum pudding, a nuclear atom, then with electrons in specific orbits, and finally with protons and neutrons in the nucleus.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
How the Atom Model Changed
Atomic structure
Lesson 3 of 10

Each new model came from new evidence.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
The Alpha Scattering Experiment
Atomic structure
Lesson 3 of 10

Most alpha particles passed straight through.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Evidence and Conclusions
Atomic structure
Lesson 3 of 10
Match each result to its explanation.
Observation
Conclusion
Most alpha particles went straight through
Most of the atom is empty space
Some were deflected through small angles
The nucleus is positive and repels the positive alpha particles
A very few bounced back
The mass is concentrated in a tiny, dense, charged nucleus
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Plum Pudding or Nuclear?
Atomic structure
Lesson 3 of 10
PLUM PUDDING MODEL
• A ball of positive charge.
• Negative electrons embedded in it.
• Charge and mass spread throughout the atom.
NUCLEAR MODEL
• A tiny, positively charged nucleus at the centre.
• Electrons orbit at a distance.
• Most of the atom is empty space.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Why the Model Changed
Atomic structure
Lesson 3 of 10
Explain why the results of the alpha scattering experiment led to the plum pudding model being replaced.
1
Plum pudding prediction
Alpha particles should pass through with only small deflections
2
Result
Some were deflected by large angles and a few rebounded
3
Conclusion
A concentrated, positive nucleus must exist, so the nuclear model replaced the plum pudding model
ANSWER
The scattering results could not be explained by the plum pudding model, so the nuclear model replaced it.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
The Story
Atomic structure
Lesson 3 of 10
Learn the sequence.
Before the electron
Atoms were thought to be tiny spheres that could not be divided.
Discovery of the electron
Led to the plum pudding model.
Alpha scattering
Led to the nuclear model; the nucleus was charged.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
The Story (cont.)
Atomic structure
Lesson 3 of 10
Bohr
Adapted the nuclear model with electrons orbiting at specific distances; his calculations agreed with experiments.
Protons
The nucleus's charge was divided into whole-number units: protons.
Chadwick
Provided evidence for neutrons about 20 years after the nucleus was accepted.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Key Terms
Atomic structure
Lesson 3 of 10
Model
A representation used to explain observations.
Plum pudding model
A ball of positive charge with electrons embedded.
Alpha scattering
An experiment in which alpha particles are fired at gold foil.
Nuclear model
An atom with a small, dense, positive nucleus.
Bohr model
Electrons orbit the nucleus at specific distances.
Evidence
Experimental results that support or contradict a model.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Atomic structure
Lesson 3 of 10
YOUR TASK
Predict the Result
12 minutes
If the plum pudding model were correct, what would happen to alpha particles fired at gold foil? What actually happened, and what did it show?
1
Predict with plum pudding.
2
Compare with the result.
WHAT A GOOD ANSWER SHOWS
They would pass through with small deflections. In fact most passed straight through, some were deflected by large angles and a few bounced back, showing a small dense positive nucleus.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Can I...?
Atomic structure
Lesson 3 of 10
Describe the plum pudding model.
Describe the nuclear model.
Describe the alpha scattering results.
Explain why the model changed.
Say what Bohr added.
Say what Chadwick showed.
Explain why models change.
Order the models.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Summary & Exam Focus
Plum pudding: ball of positive charge with electrons in it.
Nuclear: small positive nucleus with electrons around it.
Alpha scattering evidence changed the model.
Bohr: specific orbits. Chadwick: neutrons.
EXAM FOCUS
Describe the difference between the plum pudding model and the nuclear model of the atom. (3 marks)
Say where the positive charge and mass are in each.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Exam Practice: The development of the model of the atom
Atomic structure
Lesson 3 of 10
Answer all questions. Use the mark allocation as a guide to how much to write. · 18 minutes
Question 1 · 2 marks · Describe
Describe the plum pudding model of the atom.
Question 2 · 4 marks · Explain
The diagram shows the paths of alpha particles fired at thin gold foil. Explain how these results led to the nuclear model of the atom.
Question 3 · 3 marks · Describe
Describe how the nuclear model of the atom differs from the plum pudding model.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Exam Practice: The development of the model of the atom (cont.)
Atomic structure
Lesson 3 of 10
Question 4 · 2 marks · State
State two ways in which Bohr changed the nuclear model, or what the later experiments showed.
Question 5 · 6 marks · Explain
Describe how the model of the atom has changed, from the idea of a solid sphere to the model with protons and neutrons in the nucleus…
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Question 1 · 2 marks · Describe
Atomic structure
Lesson 3 of 10
“
Describe the plum pudding model of the atom.
HOW TO ANSWER IT
Command word: Describe. Worth 2 marks, so plan before writing.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Question 1 · mark scheme
Atomic structure
Lesson 3 of 10
2 marks available. Award a mark for each point made.
Ball of positive charge
1 mark
Electrons embedded in it
1 mark
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Question 2 · 4 marks · Explain
Atomic structure
Lesson 3 of 10

The diagram shows the paths of alpha particles fired at thin gold foil. Explain how these results led to the nuclear model of the atom. (4 marks)
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Question 2 · mark scheme
Atomic structure
Lesson 3 of 10
4 marks available. Award a mark for each point made.
Most went straight through so the atom is mostly empty space
1 mark
Some deflected: the nucleus is positive
1 mark
A few rebounded: mass concentrated in a small nucleus
1 mark
Plum pudding could not explain this
1 mark
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Question 3 · 3 marks · Describe
Atomic structure
Lesson 3 of 10
“
Describe how the nuclear model of the atom differs from the plum pudding model.
HOW TO ANSWER IT
Command word: Describe. Worth 3 marks, so plan before writing.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Question 3 · mark scheme
Atomic structure
Lesson 3 of 10
3 marks available. Award a mark for each point made.
Nuclear: positive charge and mass in a small nucleus
1 mark
Electrons outside the nucleus
1 mark
Plum pudding: charge spread out
1 mark
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Question 4 · 2 marks · State
Atomic structure
Lesson 3 of 10
“
State two ways in which Bohr changed the nuclear model, or what the later experiments showed.
HOW TO ANSWER IT
Command word: State. Worth 2 marks, so plan before writing.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Question 4 · mark scheme
Atomic structure
Lesson 3 of 10
2 marks available. Award a mark for each point made.
Electrons orbit at specific distances
1 mark
Protons and neutrons in the nucleus
1 mark
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Question 5 · 6 marks · Explain
Atomic structure
Lesson 3 of 10
“
Describe how the model of the atom has changed, from the idea of a solid sphere to the model with protons and neutrons in the nucleus. Explain why each change was made.
HOW TO ANSWER IT
Command word: Explain. Worth 6 marks, so plan before writing.
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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Question 5 · mark scheme
Atomic structure
Lesson 3 of 10
6 marks available. Award a mark for each point made.
Level 3 (5 to 6 marks): a correct sequence (solid sphere, plum pudding, nuclear model, Bohr, protons and neutrons) with the evidence for at least three changes, including alpha scattering
5 to 6 marks
Level 2 (3 to 4 marks): at least three models named with some evidence
3 to 4 marks
Level 1 (1 to 2 marks): one or two models described
1 to 2 marks
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