Iron (Fe)
Iron is element 26, a transition metal in period 4, group 8 of the periodic table. At room temperature it is a solid.
Electron configuration [Ar] 3d6 4s2
Electrons per shell 2, 8, 14, 2
Iron data
| Atomic number | 26 |
|---|---|
| Symbol | Fe |
| Atomic mass | 55.845 u |
| Category | Transition metal |
| Group | 8 |
| Period | 4 |
| Block | d |
| State at 25 °C | solid |
| Melting point | 1811 K (1537.9 °C) |
| Boiling point | 3134 K (2860.9 °C) |
| Density | 7.874 g/cm³ |
| Electronegativity (Pauling) | 1.83 |
| Atomic radius | 125 pm |
| 1st ionization energy | 763 kJ/mol |
| Electron affinity | -16 kJ/mol |
| Oxidation states | -2, -1, +1, +2, +3, +4, +5, +6 |
| Common ion charge | 2+, 3+ |
| Discovered | Known since antiquity |
Orbital diagram
Each box is one orbital holding up to two electrons of opposite spin. Following Hund’s rule, electrons spread out singly across a subshell before pairing.
Work through iron’s configuration and its ions →
Where iron sits
Iron belongs to the transition metals. Its Pauling electronegativity of 1.83 is mid-range; see the electronegativity chart and periodic trends for context. To use its mass in a calculation, try the molar mass calculator.
Iron FAQ
What is the electron configuration of iron?
Iron (Z = 26) has the configuration 1s2 2s2 2p6 3s2 3p6 3d6 4s2. In noble-gas shorthand that is [Ar] 3d6 4s2.
How many valence electrons does iron have?
8 (2 outer s + 6 d electrons; 2 in the outermost shell).
What is the atomic mass of iron?
The standard atomic weight of iron is 55.845 u, so one mole weighs 55.845 g.
Is iron a metal?
Yes. Iron is a transition metal.
What is the charge of a iron ion?
Iron most commonly forms Fe2+ or Fe3+.