AQA A-Level Chemistry AS Paper 1, June 2022: Question 13

1 mark · Easy difficulty · Multiple Choice

Identify which statement about isotopes of an element is not correct.

Practise this question

Question

Question 13 asks: 'Which statement about isotopes of an element is not correct?' followed by four multiple choice options: A 'They have the same chemical properties.', B 'They have the same number of electrons in ions of the same charge.', C 'They have the same number of neutrons.', and D 'They have the same number of protons.' Each option has a selection box beside it.
Question text

13 Which statement about isotopes of an element is not correct?

[1 mark]

A They have the same chemical properties.

They have the same number of electrons in ions of the same

B

charge.

C They have the same number of neutrons.

D They have the same number of protons.

Mark scheme

Show the mark scheme Mark scheme table row for question 13 showing the correct answer is C (AO1) with 1 mark, corresponding to 'They have the same number of neutrons.'

13 C (AO1) 1 They have the same number of neutrons.

How to answer it

Subatomic Structure: Identifying Isotope Properties

📌 What This Question Tests

This question assesses fundamental knowledge of atomic structure from Topic 3.1.1 (Atomic Structure):

  • Definition of isotopes: Atoms of the same element with the same number of protons but different numbers of neutrons.
  • Chemical behaviour: Understanding that chemical properties depend on electron configuration, which remains unchanged between isotopes.
  • Ion formation: Calculating electron numbers in ions formed from different isotopes of the same element.
  • Negative phrasing analysis: Correctly identifying statements that are false under timed conditions.

Question 13 Breakdown

Multiple Choice Question (1 Mark)

✅ Correct Option: C

Statement: "They have the same number of neutrons."

The question specifically asks which statement is not correct. By definition, isotopes of an element have the same number of protons but a different number of neutrons (and therefore a different mass number). Because statement C is scientifically incorrect, it is the correct answer to select.

Mark Scheme: C (AO1) — 1 mark

💡 Detailed Evaluation of Options

Option Statement Validity Explanation
A They have the same chemical properties. True Chemical properties are dictated entirely by the electron arrangement (same number of outer-shell electrons). Since isotopes have identical electron configurations, they react identically.
B They have the same number of electrons in ions of the same charge. True Isotopes have the same atomic number (number of protons). In a neutral atom, protons equal electrons. If both isotopes form ions of the same charge (e.g. ³⁵Cl⁻ and ³⁷Cl⁻, both gaining 1 electron to have 18 electrons), their electron counts remain identical.
C They have the same number of neutrons. False This is incorrect: Isotopes have differing numbers of neutrons. Because the question asks for the statement that is not correct, this is the winning choice.
D They have the same number of protons. True The number of protons defines the element (atomic number, Z). All isotopes of the same element must contain the exact same number of protons.

🧠 Exam Technique: "NOT" Questions

  • Circle or highlight "NOT": Underline negative keywords immediately so your brain doesn't hunt for the first true statement.
  • Annotate T / F beside options: Label each option (A: True, B: True, C: False, D: True) before picking your final answer to avoid silly misread errors.
  • Test with real examples: When unsure about statements like B, test with concrete examples such as ³⁵Cl⁻ (17p, 18e⁻) and ³⁷Cl⁻ (17p, 18e⁻).

❌ Common Errors & Examiner Traps

  • Selecting Option A: Rushing students read "Which statement about isotopes is..." and see A ("same chemical properties"), know it's a correct chemical fact, and tick it without noticing the word not.
  • Confusing chemical vs physical properties: While isotopes share chemical properties, their physical properties (such as density, rate of diffusion, boiling point) slightly differ due to different masses.
  • Second-guessing Option B: Some students assume charge affects isotopes differently. Charge is governed only by protons vs electrons; neutrons have zero effect on ion charge.

Topics

Physical Chemistry · 3.1.1 Atomic Structure

Question and mark scheme from the AQA A-Level Chemistry examination, AS Paper 1, June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.