AQA A-Level Chemistry Paper 3, June 2018: Question 8

1 mark · Easy difficulty · Multiple Choice

Identify the conclusion that can be drawn from the back-scattering of alpha particles fired at a thin gold sheet.

Practise this question

Question

A diagram depicting the Rutherford gold foil experiment. An He2+ source fires alpha particles horizontally towards a thin vertical gold sheet positioned centrally within a circular detector ring. A point labelled Q is located on the detector ring behind and above the He2+ source, representing particles that have rebounded or deflected at a large angle backwards. The question asks what conclusion can be drawn from the detection of particles at point Q, with multiple choice options A through D.
Question text

When He2+ particles were fired at a thin sheet of gold, about 1 in 8000 of the particles were

detected at point Q.

08 What conclusion can be drawn from the detection of He2+ particles at point Q?

[1 mark]

A Gold atoms have a small, positive nucleus.

B Gold atoms have electrons in orbitals.

C Gold consists of ions in a sea of delocalised electrons.

D Gold atoms have more protons than He2+ particles.

Mark scheme

Show the mark scheme Mark scheme table showing question number 08 with the correct answer corresponding to letter A.

08 A

How to answer it

AQA A-Level Chemistry • Physical Chemistry

Rutherford's Alpha Scattering Experiment & Nuclear Structure

What this question tests

  • Understanding historical evidence for atomic structure (Rutherford's α-particle scattering experiment).
  • Linking experimental observations (backscattering/reflection of He²⁺ particles) to the physical model of the atom.
  • Deducing the properties of the atomic nucleus: concentrated positive charge and extremely small volume compared to the overall atom.

Question 08

Detection of He²⁺ particles at Point Q • Multiple Choice [1 Mark]

✅ Correct Answer

A — Gold atoms have a small, positive nucleus.

Award [1 mark] for selecting option A.

💡 Key Knowledge: The Scattering Experiment

  • The probe: He²⁺ particles are helium nuclei (alpha particles), which are relatively massive and carry a +2 positive charge.
  • Position Q: Point Q represents backscattering (deflection angles > 90°).
  • Why do they rebound? Only a massive, highly concentrated positive centre of charge could exert enough electrostatic repulsion to repel a fast-moving, positively charged He²⁺ particle backwards.
  • Why only 1 in 8000? Since so few are deflected by large angles, this positively charged nucleus must occupy an extraordinarily small fraction of the total volume of the atom (most of the atom is empty space).

🧠 Exam Technique: Elimination Strategy

Always distinguish between a scientifically true statement and the direct conclusion of the experiment:

  • A: Correct. Directly explains why positively charged particles bounce backward rarely (small + positive).
  • B: Incorrect. Electron shells and orbitals were introduced later by Bohr and quantum mechanics; scattering does not show orbitals.
  • C: Incorrect. While gold is indeed a metal with delocalised electrons, this observation does not prove metallic bonding models.
  • D: Incorrect. Gold does have more protons (79 vs 2), but simply having more protons does not explain backscattering from a point-like centre.

❌ Common Errors

  • Selecting true distractors: Students often choose C or D because they are factually correct statements taught in chemistry, forgetting that the question specifically asks for the conclusion drawn from the detection at point Q.
  • Forgetting particle charge: Forgetting that He²⁺ is positively charged. If the nucleus were negative, the particles would be attracted and absorbed or deflected toward it, not repelled backwards.

Topics

Physical Chemistry · 3.1.1 Atomic Structure

Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, June 2018. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.