AQA GCSE Combined Science: Trilogy Physics Paper 1 (Foundation), 2024: Question 7

9 marks · Standard Demand difficulty · Extended Answer

Explain how the alpha particle scattering experiment led to the replacement of the plum pudding model with the nuclear model of the atom, and identify subatomic particle properties.

Practise this question

Question

The image shows a multi-part exam question about the history and structure of the atom. Part 07.1 asks for the composition of an alpha particle. Part 07.2 provides the symbol for gold as 197 over 79 Au and asks for the number of neutrons. Part 07.3 features Figure 11, which compares the predicted results of the alpha scattering experiment using the plum pudding model (where all particles are undeflected) with the actual results (where most are undeflected, some slightly deflected, and a tiny proportion deflected through large angles). It asks for a 6-mark description of how these results led to the nuclear model. Part 07.4 is a multiple-choice question asking which scientist provided evidence for the existence of neutrons.
Question text

07 Last century, scientists used evidence from the alpha particle scattering experiment to

develop a new model of the atom.

In the experiment, alpha particles were directed towards a piece of gold foil.

07.1 What does an alpha particle consist of?

[1 mark]

197Au

07.2 A gold atom has the symbol 79 .

How many neutrons are there in this gold atom?

[1 mark]

Number of neutrons =30

07.3 The alpha particle scattering experiment led to the plum pudding model of the atom

being replaced by the nuclear model.

Figure 11 shows the results predicted by the plum pudding model and the actual

results from the alpha particle scattering experiment.

Figure 11

Describe how the actual results led to the plum pudding model of the atom being

replaced by the nuclear model.

You should include details of the plum pudding model and the nuclear model of

the atom.

[6 marks]

07.4 Scientists did not know that neutrons existed when they first did alpha particle

scattering experiments.

Which scientist did the experiments that provided evidence that neutrons exist?

[1 mark]

Tick ( ) one box.

Isaac Newton

James Chadwick

Niels Bohr

Mark scheme

Show the mark scheme The mark scheme for question 7 shows the following: 07.1 requires '2 protons and 2 neutrons' for 1 mark. 07.2 requires the answer '118' for 1 mark. 07.3 is a 6-mark level-of-response question; Level 2 (4-6 marks) requires detailed scientifically relevant facts. Indicative content includes descriptions of the plum pudding model (ball of positive charge with embedded electrons), the experimental results (most particles undeflected, some large angle deflections), and the nuclear model (mass concentrated in a charged nucleus, mostly empty space). 07.4 identifies 'James Chadwick' as the correct answer for 1 mark.

Question 7

AO /

Question Answers Extra information Mark

Spec. Ref.

07.1 2 protons and 2 neutrons ignore helium nucleus 1 AO1

6.4.2.1

AO /

Spec. Ref.

07.2 118 1 AO1

6.4.1.2

AO /

Question Answers Mark

Spec. Ref.

Level 2: Scientifically relevant facts, events or processes are 4‒6

07.3 AO1

identified and given in detail to form an accurate account.

AO3

6.4.1.3

Level 1: Facts, events or processes are identified and simply 1‒3

stated but their relevance is not clear.

No relevant content 0

Indicative content

Plum pudding model

• the atom is a ball of positive charge

• electrons are embedded in the ball

Reasons why the plum pudding model was replaced

• the results were not correctly predicted by the plum pudding

model

• the plum pudding model did not predict that some particles would

be deflected

• the large angle deflections suggest that the atom contains a

nucleus

• all deflections suggest that the nucleus is charged

• most alpha particles were not deflected suggesting that atoms

are mostly empty space

Nuclear model

• mass is concentrated in the nucleus

• the nucleus is charged

• the atom is mostly empty space

• electrons orbit the nucleus– in the nuclear model – –

AO / 19

Spec. Ref.

07.4 James Chadwick 1 AO1

6.4.1.3

Total Question 7 9

How to answer it

Atomic Structure & The Alpha Scattering Experiment

What this question tests

This question assesses your ability to recall the composition of radiation particles, calculate subatomic particles from nuclear notation, and explain how experimental evidence (the alpha scattering experiment) leads to the revision of scientific models. It also tests your knowledge of the history of the atom.

Part (a) / 07.1

Alpha Particle Composition

💡 Key Knowledge

An alpha (α) particle is identical to a Helium nucleus. It is emitted from the nucleus of unstable atoms during radioactive decay.

✅ Correct Answer

  • 2 protons
  • 2 neutrons
Award 1 mark for both particles correctly identified. Note: The examiner will ignore "helium nucleus" if you write it, but you must state the protons and neutrons to get the mark.
Part (b) / 07.2

Calculating Neutrons

Gold atom symbol: ¹⁹⁷₇₉Au

📐 Calculation Steps

  1. Identify the Mass Number (top number): 197
  2. Identify the Atomic Number (bottom number): 79
  3. Subtract: 197 - 79 = 118

✅ Correct Answer

118 neutrons

❌ Common Error

Don't confuse the numbers! The Atomic Number is the number of protons. The Mass Number is protons + neutrons. If you just write "79", you have given the number of protons, not neutrons.

Part (c) / 07.3

The 6-Mark Comparison

From Plum Pudding to the Nuclear Model

🧠 Exam Technique: The "Observation-Conclusion" Link

To reach Level 2 (4–6 marks), you must link the specific experimental results to what they proved about the atom. Use this structure:

1. The Plum Pudding Model

  • The atom is a ball of positive charge.
  • Negative electrons are embedded inside it (like fruit in a pudding).

2. The Nuclear Model

  • Mass is concentrated in a central nucleus.
  • The nucleus is positively charged.
  • The atom is mostly empty space.
  • Electrons orbit the nucleus.

✅ How the Results changed the Model

  • Observation: Most alpha particles passed straight through the foil.
    Conclusion: The atom is mostly empty space.
  • Observation: Some alpha particles were deflected at small angles.
    Conclusion: There is a positively charged centre (nucleus) that repelled the positive alpha particles.
  • Observation: A tiny proportion were deflected back at large angles.
    Conclusion: The mass of the atom is concentrated in a very small, dense nucleus.

❌ Examiner Insight

Students often lose marks by describing the models but forgetting to mention the results of the experiment shown in Figure 11. You must explain why the plum pudding model was replaced (it couldn't explain the deflections).

Part (d) / 07.4

Discovery of the Neutron

💡 Key Knowledge

The timeline of discovery is a common "recall" topic:

  • Thomson: Electrons / Plum Pudding
  • Rutherford: Nucleus / Alpha Scattering
  • Bohr: Electron shells (energy levels)
  • Chadwick: Neutrons

✅ Correct Answer

James Chadwick

Topics

Physics · Chemistry · P4: Atomic Structure · C1: Atomic Structure and the Periodic Table

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 1 (Foundation), 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.