IB Chemistry Electron Configuration: How It's Taught, Tested and Learned

Electron configuration sits in Structure 1.3 of the current IB Chemistry guide (first exams 2025) and appears in both Paper 1 and Paper 2, at SL and HL. You'll write full or condensed spdf notation, identify anomalies like chromium and copper, and link configuration to periodicity or ion formation.

The core skill is identical: spdf notation, the Aufbau principle, and the chromium/copper exceptions apply to both levels. HL goes further, using successive ionisation energy data to deduce an unknown element's configuration and applying it to deeper periodicity arguments across the d-block.

Chromium is [Ar]3d⁵4s¹ and copper is [Ar]3d¹⁰4s¹, not the [Ar]3d⁴4s² or [Ar]3d⁹4s² you'd predict from the Aufbau order. A half-filled or fully-filled 3d subshell is more stable due to exchange energy, so one electron shifts from 4s into 3d. These two are the only named exceptions the IB expects.

For cations, remove electrons from the shell with the highest principal quantum number first — not the last subshell filled. So Fe²⁺ is [Ar]3d⁶, never [Ar]3d⁴4s². For anions, keep following the normal Aufbau order and simply add the extra electrons to the next available subshell.

Don't memorise a list — use the shape of the periodic table itself. Reading left to right, top to bottom through the s, p, d and f blocks gives you the correct filling order automatically, and section 6 of the IB data booklet already shows this block structure for you.

The same handful of errors show up every mock season: forgetting the chromium/copper exceptions, removing 4s before 3d electrons when forming a cation, and miscounting total electrons after ionisation. Each is a one-mark slip that's entirely avoidable with focused practice rather than more content revision.

Expect 1-2 marks for a stand-alone configuration, split between correct notation and correct electron count. More often it appears as one step inside a larger 4-6 mark question on periodicity, ionisation energy or bonding, so a small slip here can cost marks further down the same question.

No. The current IB Chemistry guide, with first exams in 2025, only requires spdf notation — not orbital box diagrams with up/down arrows. You should still understand Hund's rule qualitatively, since it explains the chromium and copper exceptions, but you won't be asked to draw box diagrams.

Both. Paper 1 (multiple-choice, no calculator) usually tests recognising a correct configuration or spotting chromium/copper as the odd one out. Paper 2 (short-answer and extended-response, calculator allowed) tests writing configurations directly and applying them to explain ionisation energy trends or ion formation.

Yes — section 6 shows the full periodic table split into s, p, d and f blocks, which lets you work out any element's configuration without memorising the whole table. It won't hand you the finished configuration, so you still need to know the filling order and the two named exceptions.

Not dramatically. The core skill — spdf notation, knowing chromium and copper — is the same at SL and HL. HL students are pushed further, using successive ionisation energy data to deduce an unknown configuration, which raises the analytical demand rather than adding new content to memorise.

Both cover spdf notation, the Aufbau principle, and the chromium/copper exceptions to a similar depth. The main difference is context: IB places it inside Structure 1.3 and ties it tightly to periodicity and ionisation energy data across both SL and HL, while A-Level treatment varies more between exam boards.

Short, repeated practice beats one long revision session for a skill like this. A topical worksheet with fifteen to twenty configuration questions, marked against worked answers, fixes the common mistakes fast. On revisionprep.com you'll find Chemistry Revision Notes on Structure 1.3, a Topical Worksheet, and Mock Papers showing exactly how it's examined.