3.1.2—Electron configuration and position
- Syllabus
- First assessment 2025
- Objective
- 3.1.2
- Level
- SL
Configuration and Position
| Configuration evidence | Position evidence |
|---|---|
| Highest occupied energy level | Period |
| Valence-electron pattern | Group pattern |
| Outermost subshell type | s, p, d, or f block |
Read the configuration in both directions: position predicts the outer pattern, and the outer pattern identifies the position.
The configuration 1s²2s²2p⁶3s²3p⁵ ends at n = 3 and p⁵, placing the element in period 3, group 17 and the p block. Reverse the reasoning by using a table position to predict the outer configuration, then check that the total electron count matches the atomic number.
Deducing Position from Configuration
Assessment in practice
Representative question
Question 1
[Maximum number: 2]
Bismuth has atomic number 83. Deduce two pieces of information about the electron configuration of bismuth from its position on the periodic table.
Any two ofthe following:
«group 15 so Bi has» 5 valence electrons «period 6 so Bi has» 6 «occupied» electron shells/energy levels «in p-block so» p orbitals are highest occupied occupied d/f orbitals
has unpaired electrons
has incomplete shell(s)/subshell(s)
Marking guidance:
Award [1] for full or condensed electron configuration, [Xe] 4f145d106s26p3. Accept other valid statements about the electron configuration.
2 max
The Periodic Table Summary
Retrieve the route: locate an element from configuration, explain periodic and group trends, write oxide/reaction and oxidation-state answers, then connect incomplete d-sublevels to transition properties, ion configurations, and colours.
Check that every trend explanation names its particle-level cause, every equation is balanced, every oxidation state is a formal charge convention, and every transition colour uses absorbed/observed complementarity.