s, p, d, and f are types of electron sublevels within the main energy levels of an atom. Each sublevel contains a fixed number of orbitals, and each orbital can hold a maximum of two electrons with opposite spins.
The Reasoning
A main energy level, or shell, is identified by the principal quantum number . Each shell is divided into one or more sublevels: the first shell contains only an s sublevel, while higher shells contain additional sublevels.
An orbital is a region of space with a high probability of finding an electron. The crucial distinction is that a sublevel contains orbitals; a sublevel is not itself a single orbital.
| Sublevel | Number of orbitals | Maximum electrons | First possible shell |
|---|---|---|---|
| s | 1 | 2 | |
| p | 3 | 6 | |
| d | 5 | 10 | |
| f | 7 | 14 |
The capacities follow from two facts: each orbital holds two electrons, and the sublevels contain 1, 3, 5, and 7 orbitals respectively. Therefore, for example, a p sublevel holds electrons.
The sublevels also differ in shape. An s orbital is spherical, p orbitals have two lobes, and d and f orbitals generally have more complex shapes. Within a p sublevel, the three orbitals have different orientations in space.
Electron configurations show how electrons occupy these sublevels. For example, oxygen has the configuration . The superscripts show the number of electrons in each sublevel, not the number of orbitals.
A common misconception is that “2p” means one orbital. It means the entire p sublevel in the second main energy level, containing three orbitals and accommodating up to six electrons.
IB Exam Technique
This is SL and HL content from Structure 1.3: Electron configurations. When writing configurations, check that no orbital contains more than two electrons and that each sublevel does not exceed its maximum capacity.
