AQA A-Level Chemistry AS Paper 1, June 2022: Question 9

1 mark Β· Easy difficulty Β· Multiple Choice

Identify which atom has two more protons and two more neutrons than chromium-52.

Practise this question

Question

Multiple choice question 09 asking: 'Which atom has two more protons and two more neutrons than 52 24 Cr?' with options A: 54 26 Cr, B: 56 26 Cr, C: 54 26 Fe, and D: 56 26 Fe, each accompanied by an answer box.
Question text

09 52

Which atom has two more protons and two more neutrons than 24Cr?

[1 mark]

A 54

26Cr

B 56

26Cr

C 54Fe

D 56Fe

Mark scheme

Show the mark scheme Mark scheme table row for question 9 showing the correct answer as option D (AO1), award 1 mark, corresponding to 56 26 Fe.

9 D (AO1) 1 56Fe

How to answer it

Deducing Atomic Symbols from Subatomic Particles

πŸ“Œ What this question tests

This question assesses fundamental knowledge of atomic structure: interpreting isotopic nuclear notation ( ᴬZX ), determining numbers of protons and neutrons, recognizing that atomic number ( Z ) uniquely defines an element's chemical symbol, and calculating the resultant mass number ( A ).

Multiple Choice • 1 Mark

Question 09: Subatomic Composition of ⁡²₂₄Cr

Identifying an atom with two additional protons and two additional neutrons

βœ… Correct Answer

D: ⁡⁢₂₆Fe

Award 1 mark for selecting option D.

πŸ“ Step-by-Step Deduction

  1. Analyze the initial atom (⁡²₂₄Cr):
    Proton number ( Z ) = 24
    Mass number ( A ) = 52
    Neutron number ( N ) = 52 βˆ’ 24 = 28
  2. Add 2 protons:
    New proton number = 24 + 2 = 26
    Element with Z = 26 is Iron (Fe), eliminating options A and B.
  3. Add 2 neutrons:
    New neutron number = 28 + 2 = 30
  4. Calculate new mass number (A):
    New mass number = protons + neutrons = 26 + 30 = 56
    (Or directly: A_new = 52 + 2 + 2 = 56 ).
  5. Combine into isotopic notation:
    Resulting symbol = ⁡⁢₂₆Fe

πŸ’‘ Key Knowledge

  • Atomic Number (Z): Bottom number; defines the number of protons in the nucleus and determines the chemical identity of the atom on the Periodic Table.
  • Mass Number (A): Top number; equals the total number of nucleons ( protons + neutrons ).
  • Neutrons (N): Calculated as N = A βˆ’ Z .
  • Conservation of Nucleons: Any change in the number of protons or neutrons directly increases the mass number by the total number of particles added ( Ξ”A = Ξ”p + Ξ”n ).

🧠 Exam Technique & Speed Tip

  • The Mass Number Shortcut: Both protons and neutrons contribute 1 unit each to the mass number. Adding 2 protons and 2 neutrons must increase the mass number by 2 + 2 = 4 .
    52 + 4 = 56 . This immediately rules out A and C!
  • Periodic Table Check: Adding 2 protons gives an atomic number of 26. Check group/period or atomic number 26 on the Periodic Table provided in the data booklet: Z = 26 corresponds to Fe , not Cr . This rules out B!

❌ Common Errors & Distractor Traps

  • Choosing C (⁡⁴₂₆Fe): The student added 2 to the mass number (52 + 2 = 54) thinking the mass number only increased by the number of neutrons or protons, forgetting that both protons and neutrons add to mass number.
  • Choosing B (⁡⁢₂₆Cr): The student correctly calculated the numbers (26 and 56) but forgot to change the element symbol from Cr to Fe . An atom with 26 protons is never chromium.
  • Choosing A (⁡⁴₂₆Cr): A combination of both mistakes: failing to update the symbol and failing to add both nucleons to the mass number.

Topics

Physical Chemistry Β· 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.