OCR A-Level Chemistry Periodic table, elements and physical chemistry (01), June 2024: Question 14

1 mark · Medium difficulty · Multiple Choice

Identify the correct statements about chlorine and its electron configuration when it reacts in redox reactions.

Practise this question

Question

Multiple-choice question 14 stating that chlorine has the electron configuration [Ne]3s2 3p5 and asking which of three statements about redox reactions are correct: 1. It can gain one electron to form 1- ions. 2. It can lose its 3s2 electrons to form 2+ ions. 3. It can lose its 3p5 electrons to form 5+ ions. Options A, B, C, and D provide different combinations of these statements.
Question text

14 Chlorine has the electron configuration [Ne]3s23p5.

Which statement(s) about chlorine is/are correct when it reacts in redox reactions?

1 It can gain one electron to form 1– ions.

2 It can lose its 3s2 electrons to form 2+ ions.

3 It can lose its 3p5 electrons to form 5+ ions.

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 Mark scheme showing the correct answer for question 14 is D.

14 D 1

How to answer it

Chlorine Electron Configuration & Redox Behaviour

What this question tests

This question assesses your understanding of atomic electron configurations, group properties of halogens, and redox chemistry (specifically oxidation states, electron transfer, and ion formation).

Question 14 Analysis

Multiple Choice Question (Total: 1 mark)

✅ Correct Answer: D (Only 1)

Statement 1 is the only correct statement. Chlorine gains 1 electron to form the chloride ion ( Cl⁻ ) with a 1- charge.

💡 Key Knowledge

  • Chlorine has the electron configuration [Ne]3s²3p⁵ .
  • As a halogen (Group 17), it typically gains 1 electron to achieve a stable octet (noble gas configuration).
  • Halogens do not lose core or valence subshell electrons to form positive ions like 2+ or 5+ in normal chemical reactions.

🧠 Exam Technique

Evaluate each statement individually:

  • Statement 1: True. Chlorine forms Cl⁻ by gaining an electron (e.g., in reduction/disproportionation).
  • Statement 2: False. Halogens are electronegative non-metals and do not lose valence electrons to form stable 2+ cations.
  • Statement 3: False. While chlorine can exhibit positive oxidation states (such as +1, +3, +5, +7 in oxoacids like HClO₃ ), it does so by forming covalent bonds involving shared pairs of electrons, not by losing 5 electrons to form a discrete 5+ gaseous ion.

❌ Common Errors

  • Confusing positive oxidation states (found in compounds like chlorates) with forming actual positive ions.
  • Assuming non-metals can easily lose multiple electrons because they have multiple electrons in their outer subshells ( 3s²3p⁵ ).
Examiner Insight: Top-level responses quickly recognized that non-metals in Group 17 gain electrons rather than losing them to form cations. Candidates who selected option A often mistook the positive oxidation states chlorine can achieve in covalent compounds for the formation of standalone multi-positive ions.

Topics

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

Question and mark scheme from the OCR A-Level Chemistry examination, Periodic table, elements and physical chemistry (01), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.