Shells, sub-shells & orbitals
Shells, sub-shells & orbitals
🔓 CRACK IT
Think of electron structure as three levels of organisation: shells contain subshells, and subshells contain orbitals. These names describe different things, so do not use them interchangeably.
An orbital can hold up to two electrons. An s subshell contains one orbital, a p subshell three and a d subshell five. That gives capacities of 2, 6 and 10 electrons respectively. The definitions and diagram below show how the levels fit together.
When drawing where electrons go, orbitals are usually represented by boxes. Each box is one orbital and each arrow is one electron; a pair of electrons in one box has opposite spins.
- Principal energy level (shell)
- The number n. In 3p, the 3 identifies the principal energy level.
- Sub-shell
- The letter, such as s, p or d. In 3p, p is a sub-shell within level 3.
- Orbital
- A region of space occupied by up to two electrons with opposite spins.
| Sub-shell | Orbitals | Maximum electrons |
|---|---|---|
| s | 1 | 2 |
| p | 3 | 6 |
| d | 5 | 10 |
🧪 TEST IT
Work on paper. Attempt each question before opening its answer. These are original CrackingChem questions, written in AQA style.
- State the maximum number of electrons in s, p and d sub-shells. [3]
- Explain why a p sub-shell holds up to six electrons. [2]
Total: 5 marks
Show answer & marking points
- s: 2; p: 6; d: 10. [3]
- Three orbitals [1], each holding a maximum of two electrons [1].