Quantum numbers
n gives the shell, l the subshell, m the orbital and s the spin. Pick any element to see its last electron.
Try any element
Type a symbol, a name or an atomic number, add a charge such as Fe3+ or Cl-, or tap an element in the table. Orbitals fill from m = −l up, spin +½ first.
ClChlorine, Z = 17, 35.45 u
[Ne] 3s2 3p5
In full: 1s² 2s² 2p⁶ 3s² 3p⁵
- Blockp block
- Period3
- Group17
- Valence7
- Unpaired1
- MagneticPara
Last electron 3p
- n3shell
- l1p subshell
- m0orbital
- s−½spin down
n, l, m and s
| Number | Tells you | Values |
|---|---|---|
| n principal | Shell and energy | 1, 2, 3 ... |
| l azimuthal | Subshell and shape | 0 to n − 1 (s, p, d, f) |
| m magnetic | Orientation of the orbital | −l to +l, 2l + 1 values |
| s spin | Spin of the electron | +½ or −½ |
Subshells
| l | Name | Orbitals | Electrons |
|---|---|---|---|
| 0 | s | 1 | 2 |
| 1 | p | 3 | 6 |
| 2 | d | 5 | 10 |
| 3 | f | 7 | 14 |
Shells hold 2n²
| n | Subshells | Electrons |
|---|---|---|
| 1 | 1s | 2 |
| 2 | 2s, 2p | 8 |
| 3 | 3s, 3p, 3d | 18 |
| 4 | 4s, 4p, 4d, 4f | 32 |
Quantum numbers: quick answers
What are the four quantum numbers?
The principal quantum number n gives the shell and its energy, the azimuthal quantum number l gives the subshell and its shape, the magnetic quantum number m gives the orientation of the orbital, and the spin quantum number s is +½ or −½.
What values can l and m take?
For a given n, l runs from 0 to n − 1 (s, p, d, f for l = 0, 1, 2, 3). For a given l, m runs from −l to +l, so there are 2l + 1 orbitals in the subshell.
How many electrons can shell n hold?
Shell n has n² orbitals and each holds two electrons of opposite spin, so it holds 2n² electrons: 2, 8, 18 and 32 for n = 1, 2, 3 and 4.