AQA A-Level Chemistry AS Paper 1, June 2025: Question 12

1 mark · Easy difficulty · Multiple Choice

Identify the correct chronological order of the discovery of the electron, nucleus, and neutron from earliest to latest.

Practise this question

Question

Multiple-choice question 12 asking 'Which row shows the order of discovery?' from Earliest to Latest. Option A shows electron, neutron, nucleus; Option B shows electron, nucleus, neutron; Option C shows nucleus, electron, neutron; Option D shows nucleus, neutron, electron.
Question text

12 Which row shows the order of discovery?

[1 mark]

Earliest Latest

A electron neutron nucleus

B electron nucleus neutron

C nucleus electron neutron

D nucleus neutron electron

Mark scheme

Show the mark scheme Mark scheme for question 12 indicating the correct answer is B (electron, nucleus, neutron), worth 1 mark for AO1.

12 B 1 (AO1)

B electron nucleus neutron

How to answer it

Development of the Atomic Model: Order of Discovery

📋 What this question tests

This question assesses AO1 (Recall of fundamental scientific knowledge) from the atomic structure topic. Specifically, it tests your knowledge of the historical timeline and experimental breakthroughs that led to the modern understanding of the atom: the discoveries of the electron, the nucleus, and the neutron.

Question 12 • Multiple Choice

Order of Subatomic & Nuclear Discoveries

Identifying the chronological progression from earliest to latest

✅ Correct Answer

Option B: electron → nucleus → neutron

Mark Scheme: Award 1 mark for selecting option B.

The electron was discovered first (1897), followed by the nuclear model of the atom via the alpha particle scattering experiment (1911), and finally the uncharged neutron (1932).

💡 Key Knowledge (Historical Timeline)

1. Electron (1897) – J.J. Thomson
Discovered using cathode ray tubes, showing atoms contain tiny negative particles. This gave rise to the plum pudding model.
2. Nucleus (1911) – Ernest Rutherford
Discovered through the gold foil / alpha particle scattering experiment, showing mass and positive charge are concentrated in a tiny central nucleus.
3. Neutron (1932) – James Chadwick
Discovered last because it has no electrical charge, making it exceptionally difficult to detect experimentally.

🧠 Exam Technique & Elimination

  • Anchor the easiest fact: Remember that the neutron was discovered significantly later than all other parts due to its lack of charge (1932 vs ~1900).
  • Eliminate instantly: Any option where the neutron is not in the "Latest" column (Options A and D) can be struck out immediately.
  • Distinguish between Thomson and Rutherford: Thomson's electron came before Rutherford's nucleus, ruling out Option C and confirming B.

❌ Common Misconceptions

  • Confusing Rutherford with the Plum Pudding Model: Thinking the nucleus was proposed first and electrons were discovered later inside it. Thomson's plum pudding model had electrons dispersed throughout a diffuse sphere of positive charge before the dense nucleus was discovered.
  • Overlooking the difficulty of detecting neutral particles: Forgetting that the neutron took more than 20 years after the nucleus to be proven because neutral particles do not leave tracks in ionization chambers or deflect in electric/magnetic fields.

Topics

Physical Chemistry · 3.1.1 Atomic Structure

Question and mark scheme from the AQA A-Level Chemistry examination, AS Paper 1, June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.