AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), 2024: Question 1
8 marks · Standard Demand difficulty · Multiple Choice
Answer a set of multiple-choice and short-response questions about potassium covering Group 1 properties, atomic structure, ions, melting point trends, and isotopes.
Practise this questionQuestion
Question text
01 Potassium is in Group 1 of the periodic table.
01.1 What name is given to Group 1 elements?
[1 mark]
Tick ( ) one box.
Alkali metals
Halogens
Noble gases
01.2 A potassium atom is very small.
What is the radius of a potassium atom?
[1 mark]
Tick ( ) one box.
0.2 cm
0.2 mm
0.2 nm
01.3 What name is given to the number of protons in an atom?
[1 mark]
Tick ( ) one box.
Atomic number
Group number
Mass number 3
01.4 Table 1 shows the name and the relative charge of the particles in
a potassium atom.
*02* Table 1
Name of particle Relative charge
Proton
Electron –1
Complete Table 1.
[2 marks]
01.5 The electronic structure of a potassium atom is 2,8,8,1
Figure 1 represents the electronic structure of a potassium ion.
Figure 1
What is the charge on a potassium ion?
[1 mark]
Tick ( ) one box.
–1 0 4+1
01.6 Figure 2 shows the melting points of some Group 1 elements.
Figure 2
Predict the melting point of potassium.
[1 mark]
Melting point = °C 5
01.7 Potassium has two isotopes.
Table 2 shows the percentage (%) abundance of the two isotopes.
Table 2
Isotope Percentage (%) abundance
39K 93
41K 7
How is the relative atomic mass (Ar) of potassium calculated?
[1 mark]
Tick ( ) one box.
(39 × 7) + (41 × 93)
Ar =
*04* 100
(39 × 93) + (41 × 7)
Ar =
(39 × 41) + (93 × 7)
Ar =
Mark scheme
Show the mark scheme
Question 1
AO /
Question Answers Extra information Mark
Spec. Ref.
01.1 alkali metals 1 AO1
5.1.2.5
AO /
Spec. Ref.
01.2 0.2 nm 1 AO1
5.1.1.5
AO /
Spec. Ref.
01.3 atomic number 1 AO1
5.1.1.5
AO /
Question Answers Mark
Spec. Ref.
01.4 AO1
Name Relative charge
5.1.1.4
Proton +(1) 1
Neutron 0 1
Electron -1
AO /
Spec. Ref.
01.5 +1 1 AO2
5.1.1.7
5.1.2.3
5.2.1.2
AO /
Spec. Ref.
01.6 63 (°C) allow a value in the range 50–80 1 AO3
– (°C) – – 5.1.2.5
AO /
Spec. Ref. 7
01.7 (39 × 93) + (41 × 7) 1 AO2
Ar = 5.1.1.6
Total Question 1 8
How to answer it
Potassium, ions and atomic structure
What this question tests
This question checks key GCSE knowledge about the periodic table, subatomic particles, ions, trends in Group 1, and how to calculate relative atomic mass from isotopes. It rewards quick recall, reading data from a graph, and using the correct calculation method and units.
Question 1 overview
This is a mostly straightforward recall question. Most marks come from remembering definitions and using simple data from the table/graph correctly. The final part needs a formula for weighted mean atomic mass.
Part 01.1 — Name of Group 1 elements
What is given to Group 1 elements?
✅ Correct answer
Alkali metals
💡 Key knowledge
- Group 1 elements are called alkali metals.
- They include lithium, sodium, potassium, rubidium and caesium.
- They are metals and react with water to form alkaline solutions.
🧠 Exam technique
- Learn the group names exactly.
- If a multiple-choice box is used, only one option is correct.
❌ Common errors
- Choosing halogens or noble gases by mistake.
- Writing just “metals” instead of the specific name.
Part 01.2 — Radius of a potassium atom
What is the radius of a potassium atom?
✅ Correct answer
0.2 nm
💡 Key knowledge
- Atoms are extremely small, so their sizes are usually measured in nm (nanometres).
- 1 nm = 10⁻⁹ m.
- Cm and mm are far too large for an atom.
🧠 Exam technique
- Check the size scale carefully before choosing an answer.
- For atomic dimensions, the expected unit is usually nm.
❌ Common errors
- Choosing 0.2 cm or 0.2 mm because the number looks familiar.
- Ignoring the fact that atoms are much smaller than everyday objects.
Part 01.3 — Number of protons
What name is given to the number of protons in an atom?
✅ Correct answer
Atomic number
💡 Key knowledge
- The atomic number = number of protons.
- The atomic number identifies the element.
- Potassium has atomic number 19, so it has 19 protons.
🧠 Exam technique
- Remember: atomic number = protons.
- Do not confuse this with the mass number.
❌ Common errors
- Writing group number or mass number.
- Mixing up the definitions of atomic and mass number.
Part 01.4 — Relative charge of particles
Complete the table for a potassium atom.
✅ Correct answers
- Proton: +1
- Neutron: 0
- Electron: −1
💡 Key knowledge
- Protons have a relative charge of +1.
- Neutrons have a relative charge of 0.
- Electrons have a relative charge of −1.
🧠 Exam technique
- Use the correct sign.
- There is no need to write actual charge in coulombs here; the question asks for relative charge.
❌ Common errors
- Writing proton = 1 without the sign.
- Writing neutron = −1.
- Forgetting that electron charge is negative.
Part 01.5 — Charge on a potassium ion
The electronic structure of potassium is 2,8,8,1. What is the charge on a potassium ion?
✅ Correct answer
+1
💡 Key knowledge
- Potassium has 1 electron in its outer shell.
- It loses this electron to form a stable ion.
- Losing one electron gives a +1 charge.
🧠 Exam technique
- Use the electronic structure to work out the ion charge.
- Group 1 metals usually form 1+ ions because they lose one outer electron.
❌ Common errors
- Thinking the ion should be −1.
- Forgetting that metals form positive ions by losing electrons.
- Not linking the charge to the one outer electron.
Part 01.6 — Predicting the melting point of potassium
Figure 2 shows melting points of some Group 1 elements. Predict the melting point of potassium.
✅ Correct answer
63 °C
💡 Key knowledge
- Down Group 1, melting points decrease.
- Potassium is between sodium and rubidium, so its melting point should be between their values.
- Using the trend, a sensible estimate is around 63 °C.
🧠 Exam technique
- Use the trend in the graph, not exact memorisation.
- A prediction does not need to be exact, but it must be reasonable.
- State the unit: °C.
❌ Common errors
- Choosing a value that does not fit the downward trend.
- Forgetting the unit.
- Reading the graph too roughly and giving a value outside the accepted range.
Part 01.7 — Relative atomic mass of potassium
How is the relative atomic mass, Ar, calculated?
✅ Correct answer
Ar = ((39 × 93) + (41 × 7)) / 100
📐 Calculations: step-by-step
- Multiply each isotope mass by its percentage abundance.
- Add the results together.
- Divide by 100 because the percentages total 100.
Working:
Ar = ((39 × 93) + (41 × 7)) / 100
= (3627 + 287) / 100
= 3914 / 100
= 39.14
💡 Key knowledge
- Relative atomic mass is a weighted average.
- Isotopes have the same number of protons but different numbers of neutrons.
- The isotope with the higher abundance affects the answer more.
🧠 Exam technique
- Use the masses and percentages in the table exactly.
- Keep track of which number is the isotope mass and which is the abundance.
- Remember to divide by 100, not by 2.
❌ Common errors
- Using 41 × 93 and 39 × 7 the wrong way round.
- Adding the numbers without weighting them.
- Forgetting to divide by 100.
- Not showing the full calculation method.
Examiner insight: what got marks
🧠 What top answers did well
- Used exact scientific terms such as alkali metals and atomic number.
- Gave the correct particle charges with signs.
- Used the Group 1 trend to make a sensible melting point prediction.
- Applied the isotope weighted average formula correctly.
❌ Where students lost marks
- Confusing atomic number with mass number.
- Forgetting the negative sign on electron charge.
- Picking an unrealistic atomic size unit.
- Using the wrong numbers or the wrong formula for relative atomic mass.
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), 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.