OCR A-Level Chemistry AS Breadth in chemistry (01), June 2023: Question 4

1 mark · Easy difficulty · Multiple Choice

Identify the number of p-orbitals occupied by electrons in a sulfur atom

Practise this question

Question

Multiple choice question 4 asking 'How many p-orbitals are occupied by electrons in a sulfur atom?' with options A (2), B (4), C (6), and D (10), along with a box for the answer.
Question text

4 How many p-orbitals are occupied by electrons in a sulfur atom?

A 2

B 4

C 6

D 10

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme for question 4 indicating the correct answer is C, worth 1 mark, with AO1.1 assessment objective.

4 C 1 AO1.1 ALLOW 6

How to answer it

Counting Occupied p-Orbitals in a Sulfur Atom

What this question tests

This question assesses your understanding of electron configuration, atomic structure, and the distinction between subshells, orbitals, and electrons (Assessment Objective AO1.1: Demonstrate knowledge and understanding of scientific ideas).

Question Breakdown

Multiple Choice Question (Total: 1 mark)

✅ Correct Answer

C (6)

Mark Scheme: C

💡 Key Knowledge

  • Sulfur has an atomic number ($\text{Z}$) of 16, meaning it has 16 electrons.
  • Full electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁴
  • Every p-subshell contains 3 separate orbitals ( px , py , pz ).
  • Sulfur contains p-electrons in both the 2p and 3p principal energy levels.

🧠 Exam Technique

Do not confuse the number of electrons in p-orbitals with the number of orbitals themselves! Break down the occupied p-subshells step-by-step before answering.

❌ Common Errors

  • Answering B (4): Mistaking the number of electrons in the outer 3p subshell for the number of occupied orbitals.
  • Answering D (10): Confusing the maximum total capacity of electrons that p-orbitals can hold across those levels rather than the count of orbitals.

📐 Step-by-Step Breakdown

  1. Write out the full electron configuration for sulfur (16 electrons):
    1s² 2s² 2p⁶ 3s² 3p⁴
  2. Identify all principal energy levels containing p-subshells:
    Both the 2p subshell and the 3p subshell contain electrons.
  3. Count the orbitals in each p-subshell:
    Every p-subshell consists of exactly 3 orbitals. Therefore, the 2p subshell has 3 orbitals, and the 3p subshell has 3 orbitals.
  4. Determine occupation:
    Since 2p⁶ is completely full, all 3 of its orbitals are occupied. Since 3p⁴ contains 4 electrons, according to Hund's rule, they fill 3 orbitals singly first, with 1 pairing up—meaning all 3 orbitals in the 3p subshell are also occupied.
  5. Calculate total occupied p-orbitals:
    3 (from 2p ) + 3 (from 3p ) = 6 occupied p-orbitals.

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 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.