Iron (Fe)
[Ar] 3d⁶ 4s². 4 unpaired electrons, period 4, group 8, d block.
Element or ion
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.
FeIron, Z = 26, 55.845 u
[Ar] 3d6 4s2
In full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s²
- Blockd block
- Period4
- Group8
- Valence8
- Unpaired4
- MagneticPara
Last electron 3d
- n3shell
- l2d subshell
- m−2orbital
- s−½spin down
Step by step
- Iron has 26 electrons.
- Fill in (n + l) order: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶.
- Write the subshells in order of n: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s².
- Replace the argon core with [Ar]: [Ar] 3d⁶ 4s².
Iron (Fe): the numbers
| Atomic number | 26 |
|---|---|
| Atomic mass | 55.845 u |
| Period | 4 |
| Group | 8 |
| Block | d block |
| Valence electrons | 8 |
| Unpaired electrons | 4 |
| Magnetic | paramagnetic |
| Last electron | 3d: n = 3, l = 2, m = −2, s = −1/2 |
Iron (Fe): quick answers
What is the electronic configuration of iron?
Iron has 26 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s², or [Ar] 3d⁶ 4s² in short.
How many unpaired electrons does iron have?
Iron has 4 unpaired electrons, so it is paramagnetic. Put one electron in each box of a subshell before pairing (Hund’s rule) to see them.
What are the quantum numbers of the last electron of iron?
The last electron goes into 3d: n = 3, l = 2, m = −2, s = −1/2. Orbitals fill from m = −l up, spin +½ first.