AQA GCSE Chemistry Chemistry Paper 1 (Foundation), November 2020: Question 2

✅ Correct Answer

[✓] Electron

💡 Key Knowledge

In 1897, J.J. Thomson discovered the electron. This showed that Dalton's idea of atoms being indivisible solid spheres was wrong—atoms contain smaller, negatively charged particles.

❌ Common Errors

Confusing the discovery of the electron with the discovery of the proton or neutron (Chadwick in 1932). The electron was the very first subatomic particle discovered.

✅ Correct Answer

plum pudding (model)

💡 Key Knowledge

The plum pudding model represents the atom as a sphere of diffuse positive charge with tiny negative electrons embedded within it, like raisins in a pudding.

🧠 Exam Technique

Notice Figure 2 has no central nucleus! Any diagram showing a large single positive ball with scattered minus symbols represents the plum pudding model.

✅ Correct Answer

[✓] Alpha

💡 Key Knowledge

In 1909, Rutherford, Geiger, and Marsden fired positively charged alpha particles at thin gold foil. Because some were deflected and a few bounced straight back, they deduced that the atom's positive charge was concentrated in a tiny central nucleus.

❌ Common Errors

Selecting proton or electron. While an alpha particle contains protons (it is a helium-4 nucleus), the correct specification terminology for this experiment is strictly alpha particle.

✅ Correct Answer

[✓] Bohr

💡 Key Knowledge

• Niels Bohr: Proposed electrons orbit at fixed distances (energy levels/shells).
• James Chadwick: Discovered the neutron inside the nucleus.
• Dmitri Mendeleev: Arranged the early Periodic Table by atomic weights and properties.

🧠 Exam Technique

Associate key phrases directly: "specific distances" or "energy levels" = Bohr. "Neutral particle" = Chadwick.

✅ Correct Answer

Atoms of the same element have the same atomic number because they have the same number of protons .

Atoms of the same element can have different mass numbers because they have different numbers of neutrons .

Atoms have no overall charge because they have the same number of protons and electrons .

💡 Key Knowledge

• Atomic Number (Z): Number of protons (defines the identity of an element).
• Mass Number (A): Protons + Neutrons. Isotopes have different numbers of neutrons.
• Overall Charge: Atoms are neutral because positive charges (+1 per proton) cancel out negative charges (-1 per electron).

❌ Common Errors

Writing "neutrons" for the charge cancellation question. Neutrons have zero charge and have no effect on whether an atom is electrically neutral!

✅ Correct Answer

[✓] A sports arena of radius 100 m

📐 Calculations (Step-by-Step)

Scale factor = (Radius of atom) / (Radius of nucleus)

= (1 × 10⁻¹⁰ m) / (1 × 10⁻¹⁴ m) = 10⁽⁻¹⁰ ⁻ ⁽⁻¹⁴⁾⁾ = 10⁴ = 10,000

The atom is 10,000 times larger than the nucleus.

Model nucleus radius = 1 cm

Model atom radius = 1 cm × 10,000 = 10,000 cm

10,000 cm ÷ 100 cm/m = 100 m

❌ Common Errors

Mixing up negative index subtraction. Calculating 10⁻¹⁰ ÷ 10⁻¹⁴ as 10⁻⁴ instead of 10⁴ , or forgetting that 1 m = 100 cm when converting.