AQA GCSE Chemistry Chemistry Paper 1 (Foundation), June 2023: Question 9

✅ Mark Scheme Answers

• Mark 1: A ball / sphere of positive charge
• Mark 2: With (negative) electrons embedded in it

💡 Key Knowledge

Proposed by J.J. Thomson in 1904 after his discovery of the electron. The atom was thought to be neutral overall, consisting of negative electrons randomly scattered throughout a uniform cloud or "ball" of positive charge.

❌ Common Errors & Misconceptions

• Strict Penalty: Do NOT mention protons, neutrons, or a nucleus. These were discovered much later! The mark scheme explicitly forbids them.
• Vaguely stating "it has positive and negative charges" without describing the structure (a ball of positive charge with electrons embedded).

🧠 Exam Technique

Always picture the diagram: the huge plus sign represents the ball of positive charge, while the minus symbols represent embedded electrons. Use these exact specification keywords.

✅ Correct Order

Earliest: Electrons
Middle: Protons
Latest: Neutrons

💡 Historical Timeline

• 1897 (Electron): J.J. Thomson using cathode ray tubes.
• 1917–1920 (Proton): Ernest Rutherford showed the nucleus contained positive charges.
• 1932 (Neutron): James Chadwick provided evidence for uncharged particles in the nucleus (approx. 20 years after the nucleus was accepted).

❌ Common Errors

Mixing up protons and neutrons. Remember that neutrons have no electrical charge, making them the most difficult to detect and thus discovered last.

🧠 Exam Technique

Mnemonic to remember the order: Every Person Noticed → Electron, Proton, Neutron.

✅ Mark Scheme Answers

• Number of outer shell electrons: 7 [1 mark]
• Reason: (Tennessine is in) Group 7 OR it is a halogen OR the group number equals the number of outer electrons [1 mark]

💡 Periodic Table Rule

In the periodic table, the group number corresponds to the number of electrons in an atom's outer shell:

• Group 1 = 1 outer electron
• Group 7 = 7 outer electrons

🧠 Exam Technique

Look at your Periodic Table! Element 117 (Ts) is located at the very bottom of the second column from the right—Group 7 (the Halogens). Never attempt to write out 117 electrons in shells (2, 8, 8...); always use its position on the table.

❌ Common Errors

Dependent Mark Alert: Mark 2 is dependent on Mark 1 being awarded. If you predict an incorrect number of electrons, you cannot score the reason mark.

✅ Acceptable Answers

• Time was needed for peer review
• Other scientists had to check / test / repeat the results to confirm them
• To verify the evidence independently

💡 Scientific Acceptance

Before a scientific discovery is accepted by the international community, findings must undergo rigorous peer review where independent experts check the data for errors, bias, and repeatability.

❌ Common Errors

• Vague answers like "they didn't believe them" or "it was too dangerous".
• Failing to mention the checking or testing of results by other scientists.

🧠 Exam Technique

Whenever an exam asks why a discovery took time to be accepted, the key phrase is almost always peer review or results needed to be replicated/verified by other scientists.

🧠 Sanity Check Technique

Notice that 92.4% of the element has a mass of 7, and only 7.6% has a mass of 6. Therefore, the weighted average must be very close to 7 (just slightly below it). An answer of 6.9 makes complete physical sense!

❌ Common Errors

• Forgetting to round: Leaving the answer as 6.924 loses the final mark. Always underline decimal place requirements!
• Dividing by 2 instead of 100: Calculating a simple mean (6 + 7) / 2 = 6.5 completely ignores abundances and scores 0 marks.