OCR A-Level Chemistry Periodic table, elements and physical chemistry (01), June 2024: Question 1

1 mark · Easy difficulty · Multiple Choice

Identify the correct arrangement of electrons in the p-orbitals of an oxygen atom.

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Question

Multiple choice question 1 showing the electron configuration of oxygen and four options A, B, C, and D representing electron box diagrams for p-orbitals with arrows indicating spin. Option A shows two boxes with two up arrows each and one empty box. Option B shows two boxes with paired opposing arrows and one empty box. Option C shows one box with two up arrows and two boxes with one up arrow each. Option D shows one box with paired opposing arrows and two boxes with one up arrow each.
Question text

1 Oxygen has the electron configuration 1s22s22p4.

How are the electrons in an atom of oxygen arranged in the p-orbitals?

A

↑↑ ↑↑

B

↑↓ ↑↓

C

↑↑ ↑ ↑

D

↑↓ ↑ ↑

Your answer [1]

Mark scheme

Show the mark scheme The mark scheme shows that the correct answer for question 1 is D, worth 1 mark.

1 D 1

How to answer it

Oxygen p-Orbital Electron Arrangement

What this question tests

This question assesses your understanding of quantum chemistry principles: filling subshells, Hund's rule of maximum multiplicity, and the Pauli exclusion principle using electron box diagrams for p-orbitals.

Question 1

Multiple Choice: Arrangement of electrons in oxygen p-orbitals

✅ Correct Answer: D

Option D correctly displays one orbital fully paired with opposite spins (up and down arrows) and two singly-occupied orbitals with parallel spins (both pointing up).

💡 Key Knowledge

  • Oxygen has the electron configuration 1s² 2s² 2p⁴ , meaning there are 4 electrons in the 2p subshell.
  • p-orbitals consist of three degenerate (equal energy) orbitals.
  • Hund's Rule: Orbitals are filled singly first with parallel spins before pairing occurs.
  • Pauli Exclusion Principle: Electrons in the same orbital must have opposite spins.

🧠 Exam Technique

Count the total electrons represented in the p-subshell for each option. Oxygen needs 4 electrons in total across the three boxes. Options A and C show incorrect spin pairings or electron counts, while B only shows 4 electrons grouped into two paired orbitals, violating Hund's rule.

❌ Common Errors

Students frequently lose marks or select option B by forgetting Hund's rule—pairing up electrons in the first available box instead of placing single electrons into separate degenerate orbitals first.

Mark Scheme Allocation: 1 mark awarded for selecting D.

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), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.