AQA GCSE Chemistry Chemistry Paper 1 (Foundation), June 2024: Question 10

✅ Correct Identification

• Model A: Plum pudding model [1 mark]
  (Also allowed: Thomson model)
• Model B: Bohr model [1 mark]
  (Also allowed: nuclear model, planetary model, Rutherford-Bohr model)

💡 Key Knowledge

• Model A (JJ Thomson, 1897): Discovered electrons. He pictured them embedded randomly in a sphere/cloud of diffuse positive charge.
• Model B (Niels Bohr, 1913): Adapted Rutherford's nuclear model by calculating that electrons orbit the positive nucleus at specific, fixed distances in shells (energy levels).

🧠 Exam Technique

Look at the specific visual features: Model A has scattered negative charges directly inside a single shaded ball with a central plus sign indicating distributed charge. Model B clearly shows distinct circular electron orbits (shells) around a central nucleus.

❌ Common Errors

Calling Model A the "Rutherford model" or simply "nuclear model". Rutherford proved the plum pudding model was wrong; he did not propose it.

🧠 How to Hit Level 2 (3–4 Marks)

• Structure your comparison: Mention at least 2 clear, paired differences (covering the nucleus, electron arrangement, or mass/charge location).
• Always include a similarity: Mentioning that both contain electrons or that both are neutral elevates your answer to a complete comparison.
• Use comparative language: Use words like "whereas", "in contrast", or "both" rather than just writing two disconnected lists.

❌ Common Mistakes to Avoid

• Comparing Model A with Model B: The question asks for Model A compared with the modern model, which includes subatomic details like neutrons and protons.
• Forgetting neutrons/protons: Plum pudding had neither! Stating "Model A has protons in the ball" is scientifically incorrect; protons were discovered later by Rutherford.

✅ Correct Answer

Isotopes are atoms of the same element with:

• The same number of protons [1 mark]
• A different number of neutrons [1 mark]

Alternative accepted: "Atoms with the same atomic number but different mass numbers."

💡 Why Chadwick's Discovery Mattered

James Chadwick provided experimental proof for the existence of the neutron in 1932. Until neutrons were discovered, scientists could not explain why atoms of the same element could have different masses despite having identical chemical properties.

❌ Lost Marks Checklist

• Vague references: Writing "different atomic masses" alone loses marks if the prompt specifies "refer to subatomic particles". You must mention neutrons.
• Mixing up particles: Saying "different numbers of protons" completely changes the element!
• Mentioning elements instead of atoms: Isotopes are atoms of the same element, not different elements.

🧠 Exam Tip

The question explicitly states: "Refer to subatomic particles in your answer". This is an examiner clue that your two marks come directly from naming two named particles: protons and neutrons.