AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), 2021: Question 6

8 marks · Standard Demand difficulty · Short Answer

This question covers the periodic table, atomic models, the definition of isotopes, and the calculation of relative atomic mass for potassium.

Practise this question

Question

The image contains five sub-questions (06.1 to 06.5) about the periodic table and atomic structure. Figure 11 shows a partial Mendeleev periodic table, Figure 12 shows four atomic models labeled A, B, C, and D, and Table 2 provides mass numbers and percentage abundances for two potassium isotopes.
Question text

06 This question is about the periodic table.

06.1 Figure 11 shows part of Mendeleev’s version of the periodic table.

Figure 11

Which group of elements had not been discovered when Mendeleev’s version of the

periodic table was published?

[1 mark]

Figure 12 represents different models of the atom.

Figure 12

06.2 Which model represents the plum pudding model?

[1 mark]

Tick ( ) one box.

A B C D

06.3 Which model resulted from Chadwick’s experimental work?

[1 mark]

*20* Tick ( ) one box.

A B 22C D

Potassium has different isotopes.

06.4 What is meant by ‘isotopes’?

You should refer to subatomic particles.

[2 marks]

06.5 Table 2 shows the mass numbers and the percentage abundance of two

isotopes of potassium.

*21* Table 2

Mass number Percentage abundance

39 93.1

41 6.9

Calculate the relative atomic mass (Ar) of potassium.

Give your answer to 1 decimal place.

[3 marks]

Relative atomic mass (1 decimal place) =

Mark scheme

Show the mark scheme The mark scheme provides the answers for questions 06.1 through 06.5, detailing the expected responses for identifying the noble gases, the plum pudding model, Chadwick's model, the definition of isotopes, and the calculation for relative atomic mass.

AO /

Question Answers Extra information Mark

Spec. Ref.

06.1 (Group) 0 1 AO2

or 5.1.2.2

noble gases

06.2 B 1 AO2

5.1.1.3

06.3 A 1 AO3

5.1.1.3

06.4 (atoms with the) same number allow atoms with the same 1 AO1

of protons atomic number 5.1.1.5

allow atoms of the same

element

ignore the same number of

electrons

(but with) different numbers of ignore (but with) different mass 1

neutrons numbers

do not accept (but with) different

relative atomic mass

06.5 (39 × 93.1) + (41 × 6.9) AO2

100 5.1.1.6

= 39.138 1

= 39.1 allow correctly rounded answer 1

to 1 decimal place from an

incorrect calculation using all the

values given in the question

Total 8

How to answer it

Atomic Structure & The Periodic Table

What this question tests

This question assesses your understanding of the history of the periodic table, the evolution of atomic models (from Dalton to Chadwick), the definition of isotopes using subatomic particles, and the mathematical skill of calculating Relative Atomic Mass (Aᵣ) from abundance data.

Question Part 06.1

Mendeleev's Periodic Table

💡 Key Knowledge

Dmitri Mendeleev published his table in 1869. He left gaps for elements he predicted existed, but one entire group was missing because they are inert (unreactive) and hadn't been detected yet.

✅ Correct Answer

Group 0

OR

Noble Gases

[1 mark]
Question Parts 06.2 & 06.3

History of the Atom

🧠 Identifying the Models

  • Model C: Dalton (Solid sphere).
  • Model B: Plum Pudding (Positive "dough" with negative electrons).
  • Model D: Rutherford (Nuclear model - positive nucleus, empty space).
  • Model A: Chadwick/Bohr (Modern model with neutrons and shells).

✅ Correct Answers

06.2 (Plum Pudding): Model B

06.3 (Chadwick): Model A

[2 marks total]

❌ Common Errors

Students often confuse Rutherford (Model D) with Chadwick (Model A). Remember: Chadwick discovered the neutron. If the diagram shows two types of particles in the nucleus (protons and neutrons), it represents the work of Chadwick.

Question Part 06.4

Defining Isotopes

💡 Key Knowledge

Isotopes are versions of the same element. Because they are the same element, they must have the same number of protons. The only difference is their mass, which is caused by the number of neutrons.

✅ Correct Answer

  • Atoms with the same number of protons [1 mark]
  • But with different numbers of neutrons [1 mark]

🧠 Exam Technique

The question explicitly says "refer to subatomic particles". If you only say "different mass numbers," you may lose marks. Always specify protons and neutrons to be safe.

Question Part 06.5

Calculating Relative Atomic Mass (Aᵣ)

📐 Step-by-Step Calculation

To find the average mass, we multiply each mass by its percentage, add them together, and divide by 100.

  1. Multiply mass by abundance:
    (39 × 93.1) = 3630.9
    (41 × 6.9) = 282.9
  2. Add the results:
    3630.9 + 282.9 = 3913.8 [1 mark]
  3. Divide by 100:
    3913.8 / 100 = 39.138 [1 mark]
  4. Round to 1 decimal place:
    39.1 [1 mark]

❌ Calculation Traps

  • Rounding: The question specifically asks for 1 decimal place. Writing "39.138" or "39" would lose the final mark.
  • Sanity Check: Potassium-39 is much more abundant (93.1%) than Potassium-41. Therefore, your answer must be very close to 39. If you get 40.5, you know you've made a mistake!

🧠 Examiner Insight

Top-level responses show the full working out. Even if you make a small typing error in your calculator, showing the formula (mass × %) + (mass × %) / 100 can often earn you "method marks" even if the final answer is wrong.

Topics

Chemistry · C1: Atomic Structure and the Periodic Table

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 1 (Foundation), 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.