AQA A-Level Chemistry AS Paper 1, November 2021: Question 24

1 mark · Medium difficulty · Multiple Choice

Identify which of the given elements has a first ionisation energy lower than that of sulfur.

Practise this question

Question

Multiple choice question 2.4 asking which element has a first ionisation energy lower than that of sulfur, with options A Chlorine, B Oxygen, C Phosphorus, and D Selenium.
Question text

24 Which element has a first ionisation energy lower than that of sulfur?

[1 mark]

A Chlorine

B Oxygen

C Phosphorus

D Selenium

Mark scheme

Show the mark scheme Mark scheme indicating the correct answer is D (Selenium) for 1 mark.

24 D 1 Selenium

How to answer it

First Ionisation Energy Trends

What this question tests

This question assesses your understanding of periodic trends in first ionisation energy—specifically looking at trends down a group versus across a period, and factoring in nuclear charge, atomic radius, and shielding.

Question Part 2.4

Comparing First Ionisation Energies

✅ Correct Answer

D) Selenium

Mark: 1 / 1

💡 Key Knowledge

  • Down a group: First ionisation energy decreases because atomic radius increases and inner-shell electron shielding increases, outweighing the increased nuclear charge.
  • Across a period: First ionisation energy generally increases due to increasing nuclear charge and decreasing atomic radius with similar shielding.
  • Sulfur (S) is in Period 3, Group 6. Selenium (Se) is directly below sulfur in Group 6 (Period 4).

🧠 Exam Technique

  • Locate sulfur (S) on your Periodic Table first.
  • Systematically check the given options: Chlorine (Cl) and phosphorus (P) are in Period 3 (further right/left), oxygen (O) is higher up in Group 6 (Period 2), and selenium (Se) is down in Group 6 (Period 4).
  • Remember that descending a group always results in a lower first ionisation energy due to added electron shells.

❌ Common Errors

  • Choosing Oxygen (B) by confusing periodic table directions—oxygen is in the same group as sulfur, but higher up, meaning it has a higher ionisation energy.
  • Choosing Chlorine (A) or Phosphorus (C) by incorrectly assuming elements further across the period always have lower values.

Topics

Inorganic Chemistry · 3.2.1 Periodicity

Question and mark scheme from the AQA A-Level Chemistry examination, AS Paper 1, November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.