1.3.4—Sublevels
- Syllabus
- First assessment 2025
- Objective
- 1.3.4
- Level
- HL
Sublevels, Orbitals, and Blocks
A main energy level contains only the sublevels allowed by its principal quantum number: n = 1 has s; n = 2 has s and p; n = 3 has s, p and d; and n = 4 can include s, p, d and f. Within one main level the sublevels rise in energy s < p < d < f, while the filling order across different levels can interleave, as the next card makes explicit. Each sublevel contains a fixed number of orbitals.
| Sublevel | Number of orbitals | Maximum electrons | Assessed shape evidence | Periodic-table block |
|---|---|---|---|---|
| s | 1 | 2 | spherical | s block |
| p | 3 | 6 | three dumbbell orbitals with different orientations | p block |
| d | 5 | 10 | shape detail not required here | d block |
| f | 7 | 14 | shape detail not required here | f block |
The block is identified by the subshell being filled; sublevel capacity is not the same as actual occupancy.
For recognition questions, keep the hierarchy clear: main energy level → sublevel → orbital. The s and p shapes are the explicitly required shape evidence here.
Use the hierarchy as a classification test: a p sublevel contains three orbitals, and each orbital can hold two electrons. An orbital describes a probability region with a characteristic shape; it is not a circular route travelled by an electron.
Recognising Orbital Shapes
Assessment in practice
1–2 marks in the two selected direct examples marksHow it is assessed
Questions ask students to recognize or sketch the characteristic s-orbital sphere and p-orbital dumbbell, with labels where required.
Command terms
sketch
What earns marks
Match each orbital label to its shape and show the p-orbital lobes with the correct orientation; keep the orbital-shape model distinct from the number of orbitals in a sublevel and from the periodic-table block label.
Watch for
Drawing an s orbital as a dumbbell or a p orbital as a sphere
Representative question
Question 1
[Maximum number: 2]
Sketch the shapes of two different orbital types in the second energy level and label each orbital.
s-orbital
p-orbital
correct shape AND label for each. .
The p orbital must be aligned with an axis and the node must be at or close to the origin.
Accept p-orbital aligned to any of the three axes.
Electron Configurations Summary
Retrieve the chain: emission lines reveal discrete levels; capacities, sublevels, orbitals, and spin rules build configurations; first and successive ionization energies then reveal how electrons are held and arranged.
When checking an answer, ask: Did I link a line to a transition? Did I use 2n² and the filling rules? Did I explain an ionization trend or count electrons before a successive-IE jump?