OCR A-Level Chemistry AS Breadth in chemistry (01), June 2023: Question 1

1 mark · Easy difficulty · Multiple Choice

Explain the trend in boiling points down the halogen group in terms of intermolecular forces.

Practise this question

Question

Multiple choice question asking which statement explains the trend in boiling points down the halogens group, with options A (covalent bonds become stronger), B (induced dipole-dipole interactions/London forces become stronger), C (ionic bonds become stronger), and D (permanent dipole-dipole interactions become stronger).
Question text

1 Which statement explains the trend in boiling points down the halogens group?

A Covalent bonds become stronger.

B Induced dipole–dipole interactions (London forces) become stronger.

C Ionic bonds become stronger.

D Permanent dipole–dipole interactions become stronger.

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme indicating the correct answer is B for 1 mark, with AO element AO1.1.

AO

Question Answer Marks Guidance

element

1 B 1 AO1.1

How to answer it

Trend in Boiling Points Down Group 7

OCR AS Level Chemistry • Multiple Choice

What this question tests

This question assesses your understanding of intermolecular forces in covalent molecules, specifically how induced dipole-dipole interactions (London forces) change as you move down Group 7 (the halogens) from fluorine to iodine, and how this directly affects physical properties like boiling points.

Question 1 Analysis

Identifying the correct statement for halogen boiling points

✅ Correct Answer: B

Induced dipole-dipole interactions (London forces) become stronger.

As you go down Group 7, molecules (e.g., F₂, Cl₂, Br₂, I₂) get larger with more electrons. This increases the size of the temporary dipoles and makes London forces stronger, requiring more thermal energy to overcome during boiling.

💡 Key Knowledge

  • Halogens exist as simple covalent diatomic molecules (X₂).
  • Boiling points depend on overcoming intermolecular forces between molecules, not breaking covalent bonds within molecules.
  • Down the group: atomic radius increases, number of electrons increases, and London forces become stronger.

🧠 Exam Technique

  • Always link physical properties of simple molecular substances (like melting/boiling points or solubility) to intermolecular forces, never to intramolecular bonding.
  • Eliminate options mentioning ionic bonds (halogens are non-metals forming covalent molecules) or permanent dipoles (halogen molecules are symmetrical and non-polar).

❌ Common Errors

  • Choosing A: Thinking that covalent bonds break when a molecular substance boils. Covalent bonds stay intact; it is the forces between molecules that break.
  • Confusing bond types: Mistakenly assuming halogens involve ionic bonding or permanent dipoles due to electronegativity misconceptions.
Mark Allocation: 1 mark available for selecting option B. (AO1.1 - Demonstrate knowledge and understanding of scientific ideas).

Topics

Module 3: Periodic table and energy · 3.1 The periodic table

Question and mark scheme from the OCR A-Level Chemistry examination, AS Breadth in chemistry (01), June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.