Edexcel A-Level Chemistry AS Paper 1, June 2024: Question 1

Mark scheme

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Question

Answer Mark

Number

1 The only correct answer is B (1s22s22p63s23p6) (1)

A is incorrect because this is the electronic configuration of a phosphorus atom

C is incorrect because this would be the electronic configuration of a P3+ ion

D is incorrect because this electronic configuration is missing the 3s orbital

(Total for Question 1 = 1 mark)

How to answer it

Electronic Configuration of the Phosphide Ion

What this question tests

This question assesses your understanding of atomic structure, specifically how to determine the electron configurations of negative ions (anions) by adding electrons to account for ionic charge, and correctly filling subshells in order of increasing energy.

Question 1 Breakdown

Edexcel AS Level Chemistry

✅ Correct Answer: B

1s² 2s² 2p⁶ 3s² 3p⁶

Phosphorus has an atomic number of 15 (15 electrons). The phosphide ion has a 3− charge, meaning it has gained 3 electrons, bringing the total to 18 electrons.

💡 Key Knowledge

Neutral phosphorus atom: 1s² 2s² 2p⁶ 3s² 3p³ (15 electrons).
P³⁻ means add 3 electrons to the outer 3p subshell.
Filling order follows Aufbau principle: fills up to 3p⁶ (isoelectronic with Argon).

🧠 Exam Technique

Always count the total number of electrons in the options when dealing with ions. For P³⁻ , look for an configuration that sums to 15 + 3 = 18 electrons before checking subshell filling order.

❌ Common Errors

Distractor A: Gives the configuration for a neutral phosphorus atom ( 15 electrons) instead of the P³⁻ ion.
Distractor C: Represents a P³⁺ positive ion (losing electrons instead of gaining).
Distractor D: Misses the 3s subshell entirely, breaking the filling sequence.

Mark Allocation: (Total for Question 1 = 1 mark) — Awarded for selecting option B.

Topics

Physical Chemistry · Topic 1: Atomic Structure and the Periodic Table