OCR A-Level Chemistry AS Breadth in chemistry (01), June 2019: Question 2

1 mark · Medium difficulty · Multiple Choice

Identify which of the given molecules contains the largest bond angle.

Practise this question

Question

Multiple choice question asking which molecule contains the largest bond angle among C2H4 (A), H2O (B), NH3 (C), and CH4 (D), with an answer box provided.
Question text

2 Which molecule contains the largest bond angle?

A C2H4

B H2O

C NH3

D CH4

Your answer [1]

Mark scheme

Show the mark scheme The mark scheme indicates that the correct answer for question 2 is A, worth 1 mark under Assessment Objective AO1.1.

2 A 1 AO1.1

How to answer it

Identifying the Molecule with the Largest Bond Angle

What this question tests

This question assesses your knowledge of Electron Pair Repulsion Theory (EPR), molecular shapes, and exact bond angles. You must be able to determine shapes and bond angles for common species by counting bonding pairs and lone pairs around the central atom.

Question 2 (Multiple Choice)

Determining Maximum Bond Angles

✅ Correct Answer

A ( C₂H₄ )

Ethene contains carbon atoms involved in a double bond with trigonal planar geometry, resulting in bond angles of approximately 120°.

💡 Key Knowledge

  • A: C₂H₄ (Ethene): Each carbon has 3 regions of electron density (trigonal planar), giving H-C-H and H-C-C angles of ~120°.
  • B: H₂O (Water): Non-linear shape with 2 bonding pairs and 2 lone pairs. Bond angle is compressed to ~104.5°.
  • C: NH₃ (Ammonia): Trigonal pyramidal shape with 3 bonding pairs and 1 lone pair. Bond angle is compressed to ~107°.
  • D: CH₄ (Methane): Tetrahedral shape with 4 bonding pairs and 0 lone pairs. Exact bond angle is 109.5°.

🧠 Exam Technique

Go through each option systematically and quickly jot down the shape and expected bond angle in your exam booklet:

  • Linear = 180°
  • Trigonal planar = 120°
  • Tetrahedral = 109.5°
  • Pyramidal = 107°
  • Non-linear = 104.5°

❌ Common Errors

Students often confuse tetrahedral angles (109.5°) with trigonal planar angles (120°) or forget that lone pairs reduce bond angles by roughly 2.5° per lone pair due to greater repulsion.

Mark Scheme Allocation: 1 mark for selecting option A (AO1.1 Knowledge).

Topics

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

Question and mark scheme from the OCR A-Level Chemistry examination, AS Breadth in chemistry (01), June 2019. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.