Edexcel A-Level Chemistry AS Paper 1, November 2020: Question 2

7 marks · Medium difficulty · Open Response

Identify equations and successive ionisation energy trends, complete a first ionisation energy trend graph for Period 3 elements, and deduce electron shells from a log successive ionisation energy graph of sodium.

Practise this question

Question

Exam question with multiple choice parts on second ionisation energy of bromine and successive ionisation energies of boron, followed by a graph-completion question for Period 3 first ionisation energies and a deduction question based on a log successive ionisation energy graph for sodium.
Question text

2 This question is about ionisation energies.

(a) (i) Which equation represents the second ionisation of bromine?

(1)

A Br(g) + e– → Br–(g)

B Br–(g) + e– → Br2–(g)

C Br(g) – 2e– → Br2+(g)

D Br+(g) – e– → Br2+(g)

(ii) Which set of successive ionisation energies is most likely to be associated with

the element boron?

(1)

A 738,1451,7733,10541,13629

B 801,2427,3660,25026,32828

C 1086,2353,4621, 6223,37832

D 1402,2856,4578, 7475, 9445

(b) (i) Complete the graph to show how the first ionisation energies of the Period 3

elements change across the period. Precise figures are not required.

(3)

First ionisation energies of the Period 3 elements

1600

1400

1200

First

ionisation 1000

energy

/ kJ mol–1 800

Na Mg Al Si P S Cl Ar

Element

(ii) The successive ionisation energies of sodium are shown on the graph.

Successive ionisation energies of sodium

5.5 *P62306A0324*

5.0

4.5

Log

ionisation

4.0

energy

3.5

3.0

2.5

01 2 3 4 5 6 7 8 9 10 11

Number of electrons removed

State what deductions can be made from this graph.

(2)

… *P62306A0424*

(Total for Question 2 = 7 marks)

Mark scheme

Show the mark scheme Mark scheme showing correct answers for the multiple choice questions, the expected points and sketch for the Period 3 first ionisation energy graph, and the required deductions regarding electron shells and jumps in successive ionisation energies for sodium.

How to answer it

Ionisation Energies Exam Mastery

What this question tests

This question assesses your understanding of ionisation energy definitions, writing correct ionic equations, interpreting periodic trends in first ionisation energies across Period 3, and analysing successive ionisation energy data to determine electronic structure and shell configurations.

Question 2 (a)(i) — (1 Mark)

Second Ionisation Energy Equation

✅ Correct Answer

D: Br⁺(g) → Br²⁺(g) + e⁻ (or written with - e⁻ on the reactant side)

💡 Key Knowledge

  • The *n*-th ionisation energy is always the removal of an electron from a gaseous ion with a charge of (n-1)+ to form an ion with a charge of n+ .
  • State symbols are mandatory: all species must be in the gaseous state ( g ).

❌ Common Errors

  • A represents first electron affinity.
  • B represents second electron affinity.
  • C incorrectly removes 2 moles of electrons simultaneously from a neutral atom.
Mark: 1/1 for selecting D.
Question 2 (a)(ii) — (1 Mark)

Successive Ionisation Energies & Group Identification

✅ Correct Answer

B ( 801, 2427, 3660, 25026, 32828 )

💡 Key Knowledge

Boron has the electronic configuration 1s² 2s² 2p¹ (Group 3). It has 3 valence electrons in its outer shell, followed by a massive jump in ionisation energy when breaking into the inner (first) quantum shell to remove the 4th electron.

❌ Common Errors

Students often fail to spot where the large multiplicative jump occurs. Option A shows a Group 2 pattern, and Option C shows a Group 4 pattern.

Mark: 1/1 for selecting B.
Question 2 (b)(i) — (3 Marks)

Period 3 First Ionisation Energy Trend

✅ Correct Answer Points

  • Point 1: Aluminium (Al) plotted below Magnesium (Mg), but above or equal to Sodium (Na). (Dips due to outer electron entering higher energy 3p subshell).
  • Point 2: General increase from Al to Si, then P; and another general increase from S to Cl to Ar.
  • Point 3: Sulphur (S) plotted below Phosphorus (P), but above or equal to Silicon (Si). (Dips due to spin-pairing repulsion in the 3p orbitals).

🧠 Exam Technique

Remember that precise numerical values are not required, but the relative positions (the two characteristic dips at Al and S) must be clearly visible on your graph.

Marks: 1 mark per bullet point constraint met.
Question 2 (b)(ii) — (2 Marks)

Deductions from Successive Ionisation Energies of Sodium

✅ Correct Answers

  • Mark 1: Large increase/jump in energy between the 1st and 2nd electrons removed, and between the 9th and 10th electrons removed.
  • Mark 2: Relates to shell structure: 1 electron in the outermost/3rd shell, 8 electrons in the 2nd shell, and 2 electrons in the innermost/1st shell (Electronic configuration: 2, 8, 1 ).

🧠 Examiner Commentary

Top-level responses explicitly link the position of the gradient jumps to specific electron shells rather than just stating numbers. Make sure to reference both jumps for full credit.

Marks: 1 mark for identifying the jumps; 1 mark for linking them to shells/configuration of sodium.

Topics

Physical Chemistry · Topic 1: Atomic Structure and the Periodic Table

Question and mark scheme from the Edexcel A-Level Chemistry examination, AS Paper 1, November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.