An s orbital is spherical, while a p orbital has two lobes and is commonly described as dumbbell-shaped. This applies to both SL and HL content in Structure 1.3, although detailed orbital representations are especially useful when explaining electron configurations.
An atomic orbital is a region of space in which there is a high probability of finding an electron. It is not a fixed path followed by an electron around the nucleus.
| Feature | s orbital | p orbital |
|---|---|---|
| Shape | Spherical | Two-lobed or dumbbell-shaped |
| Orientation | No directional orientation | Three orientations: , , and |
| First main energy level present | ||
| Orbitals per sublevel | 1 | 3 |
| Maximum electrons per sublevel | 2 | 6 |
The spherical shape of an s orbital means its electron probability distribution is the same in every direction around the nucleus. As the main energy level increases, such as from 1s to 2s, the orbital becomes larger. Higher s orbitals also contain additional regions where the probability of finding an electron is zero.
Each p orbital consists of two regions of electron probability on opposite sides of the nucleus. The nucleus lies within a nodal plane, where the probability of finding an electron is zero. The three p orbitals have the same shape and energy in an isolated atom but point along different spatial axes.
A common misconception is that the two lobes of a p orbital represent two electrons. They do not: the lobes are parts of one orbital, and that orbital can hold a maximum of two electrons with opposite spins.
Exam technique: If asked to draw or describe these orbitals, state “spherical” for s and “two-lobed” or “dumbbell-shaped” for p. Distinguish an orbital from a sublevel: one p orbital holds two electrons, but the complete p sublevel contains three orbitals and holds six electrons.
