AQA A-Level Chemistry Paper 3, June 2025: Question 25

Identifying Elements by Periodic Table Block

📌 What this question tests

This question assesses your recall and understanding of Periodicity and atomic structure:

Definition of s, p, d, and f blocks based on an element's outer/highest-energy electron sub-shell.
Navigating the AQA Data Booklet Periodic Table to locate less familiar, high-atomic-number elements starting with similar names.

Question 25

Multiple Choice – Periodic Table Classification (1 Mark)

✅ Correct Answer

B – Radon

Mark Scheme: Award 1 mark for option B (AO1 recall).

Radon (Rn) has atomic number 86 and is located in Group 0 (18) in Period 6. Because its highest energy electrons occupy a p sub-shell ( 6p⁶ ), it is classified as a p-block element.

💡 Key Knowledge

Block definition: An element belongs to the block corresponding to the sub-shell containing its highest-energy electron.
s-block: Groups 1, 2 (plus H and He in terms of electron configuration).
p-block: Groups 3 to 0 (Groups 13 to 18, excluding Helium).
d-block: Transition metals (Groups 3 to 12).
f-block: Lanthanides and Actinides (the bottom rows).

📐 Option-by-Option Breakdown

Using the AQA Periodic Table provided in the Data Booklet, locate each element to confirm its position and block:

Option	Element	Symbol & Atomic No. (Z)	Group & Region	Block
A	Radium	Ra (Z = 88)	Group 2 (Alkaline earth metals)	s-block ( [Rn] 7s² )
B	Radon	Rn (Z = 86)	Group 0 / 18 (Noble gases)	p-block ( [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶ )
C	Rhenium	Re (Z = 75)	Group 7 (Transition metal)	d-block ( [Xe] 4f¹⁴ 5d⁵ 6s² )
D	Roentgenium	Rg (Z = 111)	Group 11 (Transition metal)	d-block ( [Rn] 5f¹⁴ 6d⁹ 7s² )

🧠 Exam Technique

Use your Data Sheet: All four options begin with "R", which is designed to test your precision. Turn straight to your Data Booklet Periodic Table rather than guessing from memory.
Locate by name/symbol: Note that Radium is Ra (bottom of Group 2) and Radon is Rn (bottom of noble gases).
Elimination strategy: Since the p-block sits on the far right (Groups 3 to 0), quickly scanning the right-hand block immediately reveals Radon ( Rn ).

❌ Common Errors

Confusing Radium and Radon: Students frequently mix up Ra (Group 2, s-block) and Rn (Group 0, p-block) due to identical prefixes.
Misidentifying Helium vs other Noble Gases: Remember that while Helium is in Group 0, its configuration is 1s² (s-block). However, all other noble gases (Ne down to Rn) are definitely p-block.
Overlooking the d-block: Mistaking lesser-known transition metals like Rhenium ( Re ) or Roentgenium ( Rg ) for p-block or f-block elements.

AQA A-Level Chemistry Paper 3, June 2025: Question 25

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