Iron
transition metal · period 4 · group 8 · d-block
Iron (/ˈaɪərn/) is a chemical element with symbol Fe (from Latin: ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table.
What the numbers say
At standard temperature and pressure Iron is a solid, sitting in period 4, group 8 of the d-block.
Its melting point of 1811 K (1538 °C) is the 27th highest of the 110 elements with a measured value — mid-range among the elements.
At 7.874 g/cm³ it is the 42nd densest of 96 elements with a quoted density.
Pauling electronegativity is 1.83. Paired with oxygen (3.44) that is a difference of 1.61, which puts the bond polar covalent — oxides here tend to be semiconducting or refractory rather than salt-like.
In the solid state it takes a body-centered cubic structure — BCC packing is stronger but shows a ductile-to-brittle transition as temperature drops.
It is reported in 8 oxidation states (-2, -1, 1, 2, 3, 4, 5, 6), which sets how many distinct compounds and phases it can form.
First identified in c. 2000 BCE.
Crystal structure
Solid Iron adopts a Body-centered Cubic arrangement, in the Cubic (isometric) system — axes a = b = c, angles α = β = γ = 90°. Symmetry controls the anisotropy of stiffness and thermal expansion, and the available slip systems set how far the metal deforms before it fractures.
Where iron shows up in engineering materials
1 entry in the materials library names it directly:
- Ductile iron EN-GJS-400-15 — Cast iron
Crystallographic examples
Iron or one of its compounds is a textbook example for these crystal systems:
- Cubic (isometric) — Cu, Al, Fe-α (BCC), NaCl, diamond, spinel MgAl₂O₄
- Orthorhombic — α-S, cementite Fe₃C, aragonite CaCO₃, olivine
Check it against computed structures
The structure search queries the Materials Project, OQMD and the Open Materials Database for computed crystal structures containing Fe — with DFT formation energy, hull stability and band gap where the provider publishes them.
K 2 · L 8 · M 14 · N 2
Properties
| Atomic number | 26 |
|---|---|
| Atomic mass | 55.8452 u |
| Series | transition metal |
| Group | 8 |
| Period | 4 |
| Block | d-block |
| Phase at STP | Solid |
| Density | 7.874 g/cm³ |
| Melting point | 1811 K (1538 °C) |
| Boiling point | 3134 K (2861 °C) |
| Electronegativity (Pauling) | 1.83 |
| Electron configuration | [Ar] 3d⁶ 4s² |
| Crystal structure | Body-centered Cubic |
| Oxidation states | -2,-1,1,2,3,4,5,6 |
| Discovered | c. 2000 BCE |
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See Fe in context with all 118 elements.
Working with iron in a real design?
Ask the materials chat how Fe behaves in your alloy system, what it does to weldability, and which grades to look at — with the source of every number named.