OCR A-Level Chemistry AS Breadth in chemistry (01), November 2020: Question 5

1 mark · Easy difficulty · Multiple Choice

Identify which p-block element contains atoms with one unpaired electron from a given multiple-choice list.

Practise this question

Question

Multiple choice question 5 asks which p-block element contains atoms with one unpaired electron. The options are A: Al, B: Si, C: P, and D: S. A box for the answer and the mark allocation of [1] are shown at the bottom.
Question text

5 Which p-block element contains atoms with one unpaired electron?

A Al

B Si

C P

D S

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme indicating the correct answer for question 5 is A.

5 A 1 2.1

How to answer it

Determining Unpaired Electrons in p-Block Elements

What this question tests

This question assesses your ability to recall and apply electron configurations, sub-shell filling rules (Hund's rule and the Pauli exclusion principle), and understanding of block classification within the Periodic Table.

Question 5 (Multiple Choice)

Electron Configurations and Unpaired Electrons

✅ Correct Answer: A (Aluminium, Al)

Aluminium has the full electron configuration 1s² 2s² 2p⁶ 3s² 3p¹ . Looking at its outermost sub-shell, the 3p orbital contains a single electron, meaning it has exactly one unpaired electron.

💡 Key Knowledge

  • Al (Aluminium): Outer shell 3s² 3p¹ → 1 unpaired electron.
  • Si (Silicon): Outer shell 3s² 3p² → 2 unpaired electrons (Hund's rule: fill orbitals singly first).
  • P (Phosphorus): Outer shell 3s² 3p³ → 3 unpaired electrons (one in each p orbital).
  • S (Sulphur): Outer shell 3s² 3p⁴ → 2 unpaired electrons (one orbital paired, two singly occupied).

🧠 Exam Technique

Do not waste time writing out full electron configurations from 1s upwards if you can quickly write out the outer sub-shells using the Periodic Table groups. Remember that p-sub-shells contain three separate orbitals that must be filled singly before pairing up.

❌ Common Errors

Students often misinterpret Hund's rule or rush through the electron filling for elements like Sulphur (S), incorrectly assuming elements further across the period might somehow drop back down to having a single unpaired electron due to pairing effects.

Mark Scheme Allocation: 1 mark awarded for selecting option A.

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), November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.