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H2 Chemistry 9729 · Nov 2023Chemistry (H2)Paper 1Most challenging

Paper 1 Q6 — Arranging 3s and 3p electrons

Atomic structure — identifying elements from 3s/3p occupancy; Hund’s rule

What the examiners said

“Candidates were required to know the arrangement of electrons within the 3s and 3p orbitals. Incorrect responses did not consider the element with 3s¹ or the element with 3s²3p¹ or the element with 3s²3p⁵…”

Try the question (reconstruction)

How many Period-3 elements (Na to Ar) have exactly one unpaired electron in their ground state?
Examiner report: “Wrong answers failed to consider 3s¹, 3s²3p¹ and 3s²3p⁵ elements.”

Explore — Period 3, orbital by orbital

Step across Period 3. The boxes show the 3s and 3p filling by Hund’s rule; the counter tallies unpaired electrons. Find every element with exactly one.

Hund’s rule fills the three 3p orbitals singly before pairing — that is why Cl (3p⁵) has just one unpaired electron, not three.

Original reconstruction inspired by the misconceptions described in the Singapore-Cambridge GCE A-Level H2 Chemistry 9729 November 2023 Examiner Report. Not the actual examination question. For classroom exploration.

Made by lookang, using Claude Fable 5. More resources: iwant2study.org