AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), June 2025: Question 1
11 marks · Low Demand difficulty · Short Answer
Answer questions on atomic structure, discovery of subatomic particles, relative charges, calculating relative atomic mass of isotopes, drawing electronic configurations, and comparing representations of ionic bonding.
Practise this questionQuestion
Question text
01 This question is about atoms and ions.
The model of the atom has changed over time.
01.1 In an early model, scientists thought the atom was a tiny sphere that
could not be divided.
Figure 1 represents this early model of the atom.
Figure 1
The discovery of a subatomic particle led to a change in the model in Figure 1.
Which was the first subatomic particle to be discovered?
[1 mark]
Tick ( ) one box.
Electron
Neutron
Proton 3
01.2 In a later model of the atom, most of the mass was concentrated in the
centre of the atom.
What is the name of the centre of an atom?
[1 mark]
01.3 Atoms contain three types of subatomic particle.
Draw one line from each subatomic particle to the relative charge of the particle.
[2 marks]
01.4 What is meant by the ‘atomic number of an atom’?
[1 mark]
Tick ( ) one box.
The number of neutrons only
The number of protons only
The number of neutrons + the number of protons4
01.5 Table 1 shows information about two isotopes of an element.
Table 1
Percentage (%)
Mass number
abundance
Isotope A 10 19.7
Isotope B 11 80.3
Calculate the relative atomic mass (Ar) of the element.
Use the equation:
(mass number × percentage) of isotope A + (mass number × percentage) of isotope B
Ar =
Give your answer to 1 decimal place.
[3 marks]
A5 (1 decimal place) =
r
01.6 An oxygen atom has eight electrons.
Complete Figure 2 to show the electronic structure of an oxygen atom.
[1 mark]
Figure 2
01.7 Figure 3 represents two models of sodium chloride.
Figure 3
What are two advantages of model B compared with model A?
[2 marks]
Tick ( ) two boxes.
Model B shows the 3D arrangement of the ions.
Model B shows the charges on the ions.
Model B shows the electronic structures of the ions.
Model B shows the relative sizes of the ions.
Model B shows which elements are present.
Mark scheme
Show the mark scheme
Question 1
AO /
Question Answers Extra information Mark
Spec. Ref.
01.1 electron 1 AO1
5.1.1.3
AO /
Spec. Ref.
01.2 nucleus 1 AO1
5.1.1.3
AO /
Question Answers Mark
Spec. Ref.
01.3 2 AO1
5.1.1.4
allow 1 mark for 1 or 2 correct
do not accept more than one line from a box on the left
AO /
Spec. Ref.
01.4 the number of protons only 1 AO1
5.1.1.4
AO /
Spec. Ref.
01.5 (10 × 19.7) + (11 × 80.3) allow 1 AO2
(Ar =) 197 + 883.3 5.1.1.6
100 (A =)
r
allow
1080.3
(Ar =)
= 10.803 1
= 10.8 1
AO /
Spec. Ref.
01.6 allow any combination of 1 AO2
x, , e(−), for electrons 5.1.1.7
AO /
Spec. Ref.
01.7 model B shows the 3D 1 AO3
arrangement of the ions 5.2.1.3
model B shows the relative 1
sizes of the ions
Total Question 1 11
How to answer it
Atomic Structure, Isotopes, and Models of Bonding
This question covers fundamental chemistry concepts from Topic 1 (Atomic Structure and the Periodic Table) and Topic 2 (Structure and Bonding):
- History of the Atom: Discovery of the electron and the development of the nuclear model.
- Subatomic Particles: Relative charges of protons, neutrons, and electrons, and the definition of atomic number.
- Isotopes & Calculations: Calculating relative atomic mass (Ar) from isotopic abundance and mass numbers to 1 decimal place.
- Electronic Structure: Drawing electron configurations across electron shells (2, 6 for oxygen).
- Scientific Models: Evaluating representations of ionic giant lattices (space-filling 3D lattice vs. dot-and-cross diagram).
First Subatomic Particle Discovered
AQA Specification 5.1.1.3 • [1 Mark]
✅ Correct Answer
Electron [1 mark]
💡 Key Knowledge
In 1897, J.J. Thomson discovered the electron. This showed atoms were not indivisible spheres, leading directly from the Dalton model to the plum pudding model.
❌ Common Errors
Confusing the electron with the proton or neutron. The neutron was discovered much later by James Chadwick in 1932.
Name of the Centre of an Atom
AQA Specification 5.1.1.3 • [1 Mark]
✅ Correct Answer
nucleus [1 mark]
💡 Key Knowledge
Rutherford's alpha particle scattering experiment proved that the mass and positive charge are concentrated in a tiny central area called the nucleus.
❌ Common Errors
Spelling errors such as writing "neutron" instead of nucleus, or confusing biological cell terminology.
Relative Charges of Subatomic Particles
AQA Specification 5.1.1.4 • [2 Marks]
✅ Correct Matching
- Electron ➔ −1
- Neutron ➔ 0
- Proton ➔ +1
• All 3 lines correct = 2 marks
• 1 or 2 lines correct = 1 mark
🧠 Exam Technique
The instructions state: "Draw one line from each subatomic particle". If you draw two lines from a single particle box, the mark scheme says do not accept more than one line from a box on the left.
💡 Quick Memory Aid
• Proton = Positive (+1)
• Neutron = Neutral (0)
• Electron = Negative (−1)
Definition of Atomic Number
AQA Specification 5.1.1.4 • [1 Mark]
✅ Correct Answer
The number of protons only [1 mark]
💡 Atomic Number vs. Mass Number
- Atomic number: number of protons (defines the element).
- Mass number: number of protons + neutrons.
❌ Common Trap
Ticking "The number of neutrons + the number of protons" — this is the mass number, not the atomic number.
Calculating Relative Atomic Mass (Ar)
AQA Specification 5.1.1.6 • [3 Marks]
📐 Step-by-Step Calculation
Formula given: Ar = [(mass number × percentage) of isotope A + (mass number × percentage) of isotope B] ÷ 100
- Step 1 (Substitution):
Ar = [(10 × 19.7) + (11 × 80.3)] ÷ 100
Ar = [197 + 883.3] ÷ 100 = 1080.3 ÷ 100 [1 mark] - Step 2 (Evaluate value):
Ar = 10.803 [1 mark] - Step 3 (Round to 1 decimal place as requested):
10.803 rounds to 10.8 [1 mark]
Final Answer: 10.8
🧠 Exam Technique & Plausibility Check
Notice that the abundances are roughly 20% mass 10 and 80% mass 11. The answer must lie between 10 and 11, and much closer to 11. An answer of 10.8 makes complete physical sense!
❌ Common Errors
- Forgetting to round to 1 decimal place (leaving it as 10.803 loses the final mark).
- Entering the equation incorrectly into a calculator without brackets (e.g. only dividing the second term by 100).
Electronic Structure of Oxygen
AQA Specification 5.1.1.7 • [1 Mark]
✅ Correct Answer
8 electrons in total arranged as:
- 2 electrons on the inner shell
- 6 electrons on the outer shell
Any clear symbol accepted: dots (•), crosses (×), or circles (o).
🧠 Exactly What to Draw
On Figure 2: draw 2 crosses spaced out on the inner circle, and 6 crosses evenly spaced (or in pairs) around the second circle.
❌ Common Errors
- Putting all 8 electrons on the outer shell (the first shell can only hold up to 2).
- Miscounting and drawing 6 electrons in total (confusing the outer shell electrons with the total electrons).
Evaluating Models of Sodium Chloride
AQA Specification 5.2.1.3 • [2 Marks]
✅ Correct Answers (Tick two boxes)
- ☑ Model B shows the 3D arrangement of the ions. [1 mark]
- ☑ Model B shows the relative sizes of the ions. [1 mark]
💡 Model Comparison Guide
- Model A (Dot-and-cross): Shows electron transfer and charges, but does NOT show the 3D crystal lattice structure or relative sizes.
- Model B (Space-filling 3D): Shows how ions pack together in three dimensions and that Cl⁻ is larger than Na⁺, but does NOT show electron structures.
❌ Why the Other Options are Incorrect
- "Shows the charges" — Both models show charges (+ and −), so this is not an advantage of B over A.
- "Shows electronic structures" — Model A shows this, not Model B.
- "Shows which elements are present" — Model A clearly labels Na and Cl; Model B does not label the elements.
Topics
Chemistry · C1: Atomic Structure and the Periodic Table · C2: Bonding, Structure and the Properties of Matter
Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 1 (Foundation), June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.