OCR A-Level Chemistry Periodic table, elements and physical chemistry (01), November 2021: Question 13

1 mark · Medium difficulty · Multiple Choice

Identify the correct statement(s) that explain the trend in boiling points down the halogens group.

Practise this question

Question

Multiple choice question 13 asking which statement(s) explain the trend in boiling points down the halogens group. Three statements are listed: 1, The induced dipole-dipole interactions (London forces) become stronger; 2, The covalent bonds become stronger; 3, The permanent dipole-dipole interactions become stronger. Four options are given: A (1, 2 and 3), B (Only 1 and 2), C (Only 2 and 3), and D (Only 1), with an answer box provided at the bottom left.
Question text

13 Which statement(s) explain(s) the trend in boiling points down the halogens group?

1: The induced dipole–dipole interactions (London forces) become stronger.

2: The covalent bonds become stronger.

3: The permanent dipole–dipole interactions become stronger.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer [1]

Mark scheme

Show the mark scheme The mark scheme indicates the correct answer is D, corresponding to option 1 only, worth 1 mark under assessment objective AO1.1.

13 D 1 AO1.1 Accept 1

How to answer it

Boiling Points Down Group 7 (Halogens)

What this question tests

This question assesses your understanding of intermolecular forces versus intramolecular bonding, specifically how the physical properties of halogens (Group 7) change down the group and the origin of London forces in simple molecular lattices.

Question 13

Multiple Choice Analysis

✅ Correct Answer: D (Only 1)

As you go down Group 7 from fluorine to iodine, the molecules increase in size and number of electrons. This leads to larger, stronger induced dipole-dipole interactions (London forces) between molecules, requiring more energy to overcome during boiling.

💡 Key Knowledge

  • Halogens exist as diatomic molecules (F₂, Cl₂, Br₂, I₂).
  • Boiling a molecular substance involves overcoming intermolecular forces, NOT breaking covalent bonds.
  • More electrons mean more polarisable electron clouds, increasing the strength of London forces.

🧠 Exam Technique

Always distinguish carefully between intramolecular bonds (covalent bonds holding atoms together within the molecule) and intermolecular forces (forces acting between separate molecules). Boiling and melting points of simple molecular substances depend on the latter.

❌ Common Errors

  • Statement 2 trap: Covalent bonds actually weaken down the group as atomic radius increases and bonding pairs are held further from the nucleus, but more importantly, covalent bonds are not broken when a halogen boils!
  • Statement 3 trap: Halogen molecules (X₂) are homonuclear and non-polar, meaning they do not possess permanent dipoles; therefore, permanent dipole-dipole interactions do not apply here.
Mark Scheme Allocation: 1 mark for selecting D (AO1.1 - Demonstration of knowledge).

Topics

Module 3: Periodic table and energy · Module 2: Foundations in chemistry · 3.1 The periodic table · 2.2 Electrons, bonding and structure

Question and mark scheme from the OCR A-Level Chemistry examination, Periodic table, elements and physical chemistry (01), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.