OCR A-Level Chemistry AS Breadth in chemistry (01), June 2022: Question 23

9 marks · Medium difficulty · Structured Questions

Describe ionic and metallic bonding, complete a magnesium sulfide lattice diagram, and name/formula oxyanions with oxidation states.

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Question text

23 This question is about different types of bonding.

(a) Ionic compounds have ionic bonding and exist in a giant ionic lattice structure.

(i) What is meant by ionic bonding?

… [1]

(ii) Magnesium reacts with sulfur to form a compound which has a giant ionic lattice

structure.

The diagram shows ions as circles in part of the lattice.

Complete the diagram by showing the symbols of the ions, including charges.

[2]

(b) ‘Oxyanions’ are ions containing oxygen combined with atoms of other elements.

Roman numerals are used to show the oxidation state of the element in the oxyanion.

Complete the table below for three oxyanions.

One row has been completed as an example.

Name of oxyanion Ionic charge Formula of oxyanion

1– BrO –

… 2

Sulfate(VI) 2– SO 2–

Phosphate(V) 3–

[2]

You may wish to include a labelled diagram in your answer.

… [4]

Mark scheme

Show the mark scheme

Question Answer Marks Guidance

element

23 (a) (i) (Electrostatic) attraction between 1 AO1.1 Attraction is essential

oppositely charged OR + and – ions ×1 IGNORE references to metal and non-metal

(ii) 2 AO1.2 ALLOW labels if seen outside circles provided it

×2 clear which circle the label applies to

ALLOW 1 mark for Mg AND S shown alternately,

each in FOUR circles

i.e. with no charges or incorrect charges

ALLOW 1 mark for 2+/+2 AND 2–/–2 shown

alternately in FOUR circles (with no Mg and S)

DO NOT ALLOW All circles with same ion,

i.e. all Mg2+ OR all S2–

Mg2+ shown alternately in FOUR circles

ALLOW 1 mark for 4 Mg2+ AND 4S2– but NOT

2– shown alternately

S shown alternately in FOUR circles

e.g.

16 AO

element

(b) 2 AO3.1

Ionic Formula of ×2

Name of oxyanion

charge oxyanion

Bromate(III) 1– BrO –

Sulfate(VI) 2– SO 2–

Phosphate(V) 3– PO 3–

4 ALLOW PO –3

Structure ×4

Giant

‘Giant metallic’ gains BOTH structure and

Bonding bonding marks

Metallic (bonding)

ALLOW attraction between cations and electrons

Attraction between nucleus and electrons is CON

Particles Watch for ‘metallic’ being CONNed within

2+ /Ca2+ ions and delocalised electrons overall response

Conductivity

(Delocalised) electrons move/flow ALLOW charge flows ONLY when linked to

Idea of movement required electrons

IGNORE electrons carry charge

Delocalised can be seen anywhere IGNORE electrons are free

BUT

ALLOW mobile electrons carry charge

How to answer it

Types of Bonding Study Guide

What this question tests

This question assesses your core understanding of chemical bonding and structure types (ionic and metallic lattices), your ability to interpret chemical nomenclature using oxidation numbers (Roman numerals in oxyanions), and your knowledge of electrical conductivity mechanisms in solids.

Question 23 (a) (i)

Defining Ionic Bonding

✅ Correct Answer

Electrostatic attraction between oppositely charged ions (positive and negative ions).

💡 Key Knowledge

You must always mention attraction and oppositely charged ions. Keywords like "electrostatic" or "strong electrostatic forces" secure top marks.

❌ Common Errors

Students frequently lose the mark by referring to electron transfer (which describes how ionic bonds form, not what ionic bonding is). References to metal and non-metal atoms are also ignored by examiners.

Mark: 1 mark

Question 23 (a) (ii)

Ionic Lattice Diagram (Magnesium Sulfide)

✅ Correct Answer

Alternating arrangement of Mg²⁺ and S²⁻ ions across the four alternating circles in the provided lattice structure.

🧠 Exam Technique

Check your charges carefully. Magnesium is in Group 2 ( Mg²⁺ ) and sulfur is in Group 6 ( S²⁻ ). Ensure every circle alternates correctly with no adjacent matching ions.

❌ Common Errors

Writing formulas without charges (e.g., just "Mg" and "S") or filling all circles with the same ion will result in zero marks.

Marks: 2 marks

Question 23 (b)

Oxyanions and Oxidation States

✅ Correct Answers

Name of oxyanion (row 1): Bromate(III)
Formula of oxyanion (row 3): PO₄³⁻ (or PO4(3-) format)

💡 Key Knowledge

Roman numerals represent the oxidation state of the central atom. In Bromate(III), bromine has an oxidation state of +3. For Phosphate(V), phosphorus has an oxidation state of +5 combined with oxide ions ( O²⁻ ).

❌ Common Errors

Forgetting the negative charge on the final formula or mixing up subscript numbers when balancing oxidation states.

Marks: 2 marks

Question 23 (c)

Structure, Bonding, and Conductivity of Solid Calcium

✅ Correct Answers

Structure: Giant (metallic) lattice
Bonding: Metallic bonding
Particles: Positive calcium ions ( Ca²⁺ / cations) and delocalised electrons
Conductivity: Conducts electricity because delocalised electrons can move / flow

🧠 Exam Technique

Structure your answer clearly using headings or distinct bullet points covering all four marking points: Structure, Bonding, Particles, and Conductivity. Make sure to explicitly state that electrons move or flow for the conductivity mark.

❌ Common Errors

Stating that "electrons are free" without mentioning movement will lose the conductivity mark. Also, avoid saying "attraction between nucleus and electrons"—it must be between positive ions/cations and delocalised electrons.

Marks: 4 marks

Topics

Module 2: Foundations in chemistry · 2.2 Electrons, bonding and structure · 2.1 Atoms and reactions

Question and mark scheme from the OCR A-Level Chemistry examination, AS Breadth in chemistry (01), June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.