AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Higher), 2018: Question 2

8 marks · Standard Demand difficulty · Short Answer

Compare the electronic structures of sodium and chlorine, describe electron transfer when they form sodium chloride, and complete the exothermic reaction profile.

Practise this question

Question

The question page contains three linked parts about sodium and chlorine. At the top, a simplified periodic table diagram labelled Figure 2 shows sodium marked as Na on the left in Group 1 and chlorine marked as Cl on the right in Group 7, then part 02.1 asks for one difference and one similarity in their electronic structures for 2 marks. Part 02.2 asks, for 4 marks, to describe what happens when a sodium atom reacts with a chlorine atom to produce sodium chloride and specifically says to write about electron transfer. Part 02.3 states that the reaction is exothermic and shows a blank reaction profile graph labelled Figure 3 with axes for relative energy and progress of reaction, a horizontal reactants line already drawn, and space for the student to complete the curve and products level for 2 marks.
Question text

02 This question is about sodium and chlorine.

Figure 2 shows the positions of sodium and chlorine in the periodic table.

Figure 2

02.1 State one difference and one similarity in the electronic structure of sodium and

of chlorine.

[2 marks]

Difference

Similarity

02.2 Sodium atoms react with chlorine atoms to produce sodium chloride (NaCl).

Describe what happens when a sodium atom reacts with a chlorine atom.

Write about electron transfer in your answer.

[4 marks]

02.3 The reaction between sodium and chlorine is an exothermic reaction.

Complete the reaction profile for the reaction between sodium and chlorine.

[2 marks]

*05* Figure 3

Mark scheme

Show the mark scheme The mark scheme is a table for questions 02.1 to 02.3 with answer points, extra guidance, marks, and specification references. For 02.1 it awards one mark for a correct difference in outer-shell electrons between sodium and chlorine and one mark for a similarity such as both having three shells or both having incomplete outer shells. For 02.2 it gives one mark each for sodium atom loses, one outer-shell electron, chlorine atom gains, and one electron, with notes that reversed transfer limits marks and references to sharing or covalent bonding limit the answer. For 02.3 it shows the completed exothermic reaction profile as a curve rising to a peak then falling to a products line below the reactants line, worth two marks in total.

AO /

Question Answers Extra information Mark

Spec. Ref.

02.1 (difference) AO2

sodium has one and chlorine number of electrons must be 1 5.1.1.7

has seven electrons in outer correct if quoted 5.1.2.1

level / shell

or

number of electrons

(similarity)

both have three / same number allow both have 2 electrons in 1

of levels / shells inner shell

or or

have electrons in third level / both have 8 electrons in second

shell shell

or or

both have incomplete (outer) both are one electron away from

levels / shells full outer level / shell

02.2 allow marks from suitable AO1

diagram(s) 5.2.1.2

sodium (atom) loses allow moves / transfers for loses 1

do not accept sodium ion loses

one (outer shell electron) 1

chlorine (atom) gains do not accept chloride 1

one (electron) 1

transfer of 1 electron from

chlorine to sodium max 2 marks

reference to sharing or covalent

bonding max 3 marks

AO /

Spec. Ref.

02.3 AO1

5.5.1.2

ignore labels

any curve / line going up and

then down

products line below reactants

allow curve to start / finish

anywhere along reactant /

product lines

Total 8

How to answer it

Sodium and chlorine: electrons and energy profile

What this question tests

This question checks whether you can describe electron structure, explain electron transfer and ionic bonding, and recognise the shape of an exothermic reaction profile. Full marks come from using the correct science words: outer shell electron, gains/loses, and products lower than reactants.

Question 02.1 — Electronic structure of sodium and chlorine

State one difference and one similarity in the electronic structure of sodium and chlorine. [2 marks]

✅ Correct answers

  • Difference: sodium has one electron in its outer shell, chlorine has seven electrons in its outer shell.
  • Similarity: both have three shells / three energy levels.
Marking point: 1 mark for a correct difference + 1 mark for a correct similarity.

💡 Key knowledge

  • Sodium is 2,8,1 .
  • Chlorine is 2,8,7 .
  • Both are in period 3, so both have 3 shells.
  • You can also say both have an incomplete outer shell.

🧠 Exam technique

  • Use a direct comparison: “sodium has…, chlorine has…”
  • Don’t just say “they are different” — you must state what is different.
  • If you give the shell numbers, make sure they are correct.

❌ Common errors

  • Saying both have the same number of electrons overall — this is not enough on its own.
  • Mixing up outer shell and inner shell electrons.
  • Writing that chlorine has “one outer electron” — that is sodium.

Question 02.2 — What happens when sodium reacts with chlorine

Describe what happens when a sodium atom reacts with a chlorine atom. Write about electron transfer in your answer. [4 marks]

✅ Correct answer

Sodium loses one outer shell electron and chlorine gains one electron. The electron is transferred from sodium to chlorine, forming sodium ions and chloride ions.

To score full marks, the answer needs both sides of the transfer: sodium loses + chlorine gains.

💡 Key knowledge

  • Sodium atom loses 1 electron from its outer shell.
  • Chlorine atom gains 1 electron.
  • This gives both atoms a full outer shell.
  • The ions formed are attracted by electrostatic attraction, making an ionic bond.

🧠 Exam technique

  • Use the command words exactly: loses and gains.
  • To get all 4 marks, include:
    • sodium atom loses
    • one electron
    • chlorine atom gains
    • one electron
  • If you mention diagrams, draw arrows showing the electron moving from sodium to chlorine.

❌ Common errors

  • Writing that electrons are shared — that is covalent bonding, not ionic bonding.
  • Saying “chloride loses” instead of chlorine atom gains.
  • Saying sodium ion loses an electron — the mark scheme wants the atom losing the electron.

Question 02.3 — Exothermic reaction profile

Complete the reaction profile for the reaction between sodium and chlorine. [2 marks]

✅ Correct answer

The graph should show a curve that goes up first to a peak, then comes down so that the products line is below the reactants line.

Any sensible curve rising then falling earns the shape mark, as long as the products are lower than the reactants.

📐 What the completed profile should look like

  1. Start at the reactants line.
  2. Draw a curve rising to show the activation energy barrier.
  3. Then draw the curve falling.
  4. Finish with the products line lower than the reactants.

If labels are present, they may be ignored by the examiner, but the shape and relative positions matter.

🧠 Exam technique

  • “Exothermic” means energy is released to the surroundings.
  • So the products must have less energy than the reactants.
  • The curve must include the initial rise, because reactions need activation energy.

❌ Common errors

  • Drawing products above reactants — that shows an endothermic reaction.
  • Drawing a straight line down with no peak.
  • Forgetting the “hill” completely.
  • Making the products line start higher than the reactants line.

Examiner insight: how marks were awarded

💡 What distinguished top answers

  • They used the exact electron terms: outer shell, loses, gains, transferred.
  • They gave a clear comparison in 02.1 rather than vague statements.
  • For 02.3 they showed the correct energy change, not just “a bump”.

❌ Where students lost marks

  • Mixing up sodium and chlorine electrons.
  • Saying electrons are shared instead of transferred.
  • Drawing the products at the wrong energy level in the reaction profile.

🧠 Quick revision summary

  • Sodium: 2,8,1
  • Chlorine: 2,8,7
  • Reaction: sodium loses 1 electron, chlorine gains 1 electron
  • Exothermic profile: products lower than reactants

Topics

Chemistry · C1: Atomic Structure and the Periodic Table · C2: Bonding, Structure and the Properties of Matter · C5: Energy Changes

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 1 (Higher), 2018. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.