AQA A-Level Chemistry Paper 3, June 2018: Question 7

1 mark · Easy difficulty · Multiple Choice

Deduce the conclusion about atomic structure that can be drawn from alpha particles passing straight through a thin sheet of gold.

Practise this question

Question

Diagram depicting the Rutherford alpha particle scattering experiment. A helium 2+ particle source directs particles in a straight line through a thin gold sheet towards point P on the far side of a circular detector. The question asks what conclusion can be drawn from most particles being detected undeflected at point P, with four multiple-choice options: A) Gold atoms contain electrons, B) Gold atoms contain protons, C) Gold atoms contain neutrons, D) Gold atoms are mainly empty space.
Question text

In the early twentieth century the apparatus shown in the diagram was used to investigate

atomic structure. When He2+ particles were fired at a thin sheet of gold, most of the

particles were detected at point P.

07 What conclusion can be drawn from the detection of He2+ particles at point P?

[1 mark]

A Gold atoms contain electrons.

B Gold atoms contain protons.

C Gold atoms contain neutrons.

D Gold atoms are mainly empty space.

Mark scheme

Show the mark scheme Mark scheme table indicating that for question 07, the correct answer is option D.

07 D

How to answer it

Rutherford Alpha-Particle Scattering & Atomic Structure

What this question tests

This question assesses fundamental knowledge of the development of the atomic model, specifically:

  • Interpreting the observations from Rutherford's alpha-particle (He²⁺) scattering experiment.
  • Linking experimental evidence (particles passing straight through without deflection to point P) to the physical structure of an atom (the nuclear model).
  • Differentiating between what is scientifically true about atoms versus what is directly concluded from a specific observation.

Question 07

Multiple Choice — Atomic Structure & Observations

✅ Correct Answer

D: Gold atoms are mainly empty space.

Mark Scheme: 1 mark for selecting option D.

Point P is directly opposite the incoming beam of He²⁺ particles. The fact that the vast majority of alpha particles passed straight through the gold foil undeflected proves that most of the volume of each gold atom consists of empty space.

💡 Key Knowledge: The Scattering Experiment

  • He²⁺ particles (α-particles): Fast-moving, positively charged helium nuclei containing 2 protons and 2 neutrons.
  • Observation 1 (Straight through to P): Most α-particles passed straight through undeflected → The atom is mostly empty space.
  • Observation 2 (Small deflections): A few α-particles were deflected by small angles → There is a concentrated positive charge in the atom that repels positive α-particles.
  • Observation 3 (Large deflections / back-scattering): Very few (≈ 1 in 8000) bounced straight back → The positive charge and most of the atom's mass are concentrated in a tiny central core (the nucleus).

🧠 Exam Technique: "What conclusion can be drawn?"

Multiple-choice questions on this topic often include statements that are chemically true, but not the correct conclusion for the specific observation highlighted:

  • Options A, B, and C are all scientifically correct facts about gold atoms (they do contain electrons, protons, and neutrons).
  • However, the straight-line path of α-particles directly to point P does not prove the existence of neutrons (discovered by Chadwick in 1932) or protons/electrons.
  • Always match the specific observation (passing straight through undeflected) directly to the deduction (encountering nothing → empty space).

❌ Common Errors & Traps

  • Selecting B ("Gold atoms contain protons"): Students think of the nucleus being positive and jump to protons. The positive nature of the nucleus was inferred from the deflected particles, not those arriving at P.
  • Confusing the Thomson vs. Rutherford models: The Plum Pudding model assumed positive charge and mass were spread evenly. If that had been true, all particles would have experienced slight, uniform deflections rather than passing straight through to P.
  • Not reading the diagram: Missing that point P lies in a straight line from the source, indicating no deflection.

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.