CalculateQuestion 1 · Recall
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By the end you can explain the terms shell, sub-shell, orbital, principal quantum number and ground state, say how many electrons s, p and d sub-shells hold, and put the sub-shells up to 4p in order of energy.
Electrons are organised in three levels, a bit like a postal address:
| level | analogy | what it is |
|---|---|---|
| shell | town | a main energy level, numbered by the principal quantum number, n = 1, 2, 3, 4 … |
| sub-shell | street | a group of orbitals of the same type (s, p or d) within a shell |
| orbital | house | holds a maximum of two electrons |
The bigger n is, the further the shell is from the nucleus and the higher its energy.
Orbital
A region of space around the nucleus where there is a high probability of finding an electron. Each orbital can hold a maximum of two electrons, with opposite spins.
| sub-shell | orbitals | max electrons |
|---|---|---|
| s | 1 | 2 |
| p | 3 | 6 |
| d | 5 | 10 |
| shell | sub-shells | orbitals | max electrons |
|---|---|---|---|
| n = 1 | 1s | 1 | 2 |
| n = 2 | 2s, 2p | 4 | 8 |
| n = 3 | 3s, 3p, 3d | 9 | 18 |
| n = 4 | 4s, 4p (4d, 4f) | 16 | 32 |
Pattern: shell n has n sub-shells, n² orbitals and room for 2n² electrons. For H to Kr you only ever use 4s and 4p from the fourth shell.