Paper 2 Q5(b) — Ionisation energy across a period

Periodicity — successive/first ionisation energies; the Al dip and the big jump to a new shell

What the examiners said

“Common errors included the atoms being isoelectronic across the period, the outer electron of aluminium being in a 2p orbital, the 3p electron having lower energy than 3s so less energy needed to remove it, not appreciating that the drop to K was very large…”

Try the question

Across Period 3 the first ionisation energy generally rises but dips at aluminium. What causes the dip from Mg to Al?

Examiner report: “Errors: outer electron 'in 2p'; 3p lower than 3s; atoms 'isoelectronic'.”

Explore — first ionisation energy across Period 3

Hover the slider across the period to read each element’s first IE. Note the general rise, the dips at Al (3s→3p) and S (p-orbital pairing), and toggle to successive IEs to see the huge jump on reaching a new shell.

Element: Al show successive IEs of Na

Two teaching points: the Al dip (3s vs 3p) and, in successive-IE mode, the large jump when ionisation reaches a new inner shell — both features the report said candidates missed.

Original reconstruction inspired by the misconceptions described in the Singapore-Cambridge GCE A-Level H1 Chemistry 8873 November 2023 Examiner Report. Not the actual examination question. For classroom exploration.

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