OCR A-Level Chemistry Periodic table, elements and physical chemistry (01), November 2021: Question 14

1 mark · Medium difficulty · Multiple Choice

Identify the correct statements about a molecule of Cl-N=O regarding polarity, lone pairs, and bond angle

Practise this question

Question

Multiple choice question 14 asking which statements about a molecule of Cl-N=O are correct. Statement 1: It is a polar molecule. Statement 2: It contains 6 lone pairs of electrons. Statement 3: It has a bond angle of 180 degrees. The options are A (1, 2 and 3), B (Only 1 and 2), C (Only 2 and 3), and D (Only 1).
Question text

14 Which statement(s) about a molecule of Cl–N=O is/are correct?

1: It is a polar molecule.

2: It contains 6 lone pairs of electrons.

3: It has a bond angle of 180°.

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 B for question 14, worth 1 mark, assessed under AO2.1.

14 B 1 AO2.1

How to answer it

Evaluating Molecular Properties of ClNO

What this question tests

This question assesses your understanding of three-dimensional molecular shapes, bond angles using electron pair repulsion theory (VSEPR), electronegativity and dipole moments to determine polarity, and counting lone pairs in covalent molecules.

Question 14

Analysis of Statements for Cl-N=O

✅ Correct Answer: B (Only 1 and 2)

Statement 1 and Statement 2 are correct. Statement 3 is incorrect because the molecule is bent, not linear.

💡 Key Knowledge: Molecular Shape of ClNO

  • Nitrogen is the central atom bonded to Chlorine (single bond) and Oxygen (double bond).
  • Nitrogen has 5 outer shell electrons: 1 shared with Cl, 2 shared with O, leaving 1 non-bonding lone pair.
  • With 2 bonding regions (one single, one double counted as a single electron domain) and 1 lone pair, the electron pair geometry is trigonal planar, giving a bent molecular shape with a bond angle of approximately 117° (less than 120° due to lone pair repulsion).

🧠 Exam Technique

Evaluate each statement methodically by sketching a quick Lewis structure and applying VSEPR theory before looking at the multiple-choice options. Eliminate options as you verify each statement.

❌ Common Errors

  • Assuming linearity: Students often see a double bond and single bond combination and incorrectly assume a 180° bond angle (like in CO₂).
  • Miscounting lone pairs: Forgetting to count the lone pairs on the terminal atoms (Cl and O) in addition to the central nitrogen atom.
Mark Breakdown: 1 mark available for identifying option B (AO2.1 - applying chemical knowledge of bonding and structure to an unfamiliar molecule).

Detailed Statement Breakdown

Statement 1: Polarity

CORRECT. Chlorine, Nitrogen, and Oxygen all have different electronegativities (Cl = 3.0, N = 3.0, O = 3.4), and the molecule is asymmetrical due to its bent shape. The dipoles do not cancel out, making ClNO a polar molecule.

Statement 2: Lone Pairs

CORRECT. Let's count them all up:
• Chlorine has 3 lone pairs (6 electrons).
• Nitrogen has 1 lone pair (2 electrons).
• Oxygen has 2 lone pairs (4 electrons).
Total = 3 + 1 + 2 = 6 lone pairs in the entire molecule.

Statement 3: Bond Angle

INCORRECT. Because nitrogen has a lone pair in addition to the two bonding regions, it repels the bonding pairs more strongly, compressing the Cl-N-O bond angle to roughly 117° — well away from the linear 180°.

Topics

Module 2: Foundations in chemistry · 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.