Iron (Fe)

Silvery-gray metal

Iron is the backbone of modern civilization and the metal that carries oxygen in your blood, and with [Ar] 3d⁶ 4s², iron's ability to switch between Fe²⁺ and Fe³⁺ oxidation states enables electron transport in hemoglobin and cytochromes. It is the fourth most abundant element in Earth's crust.

Key metrics

Density7.87g/cm³

Melting point1,811K

Boiling point3,134K

Electronegativity1.83Pauling

Discovery

-2000discovered

Discovered by: Ancient civilizations
Reactivity profile: Rust formation
Reactivity: Medium
Bonding: Metallic

Electron configuration

\textcolor{#6b7280}{[Ar]}\; \textcolor{#22c55e}{3_{d}^{6}}\; \textcolor{#ef4444}{4_{s}^{2}}

[Ar] 3d6 4s2

Wave function

\Psi_{\text{Fe}} \approx \frac{1}{\sqrt{26!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{26}(\mathbf{r}_{26}) \right|

Probability density $|\Psi|^2$ across the Fe valence shell.

Crystal structure

Body-Centered Cubic

Lattice constantsa = 1.00

Cell anglesα = β = γ = 90°

Coordination number8

Atoms per cell2

Atomic packing factor0.68

Physical properties

Atomic radius: 126 pm
Ionization energy: 762 kJ/mol
Electron affinity: 16 kJ/mol
Crystal structure: Body-centered cubic (bcc)

Oxidation states

+2+3

Acid/base

Basic

Strongly acidicStrongly basic

State at 25 °CSolid

1811 K3134 K298 K

Emission spectrum

4 transitions

380450500550600650700780

VioletBlueGreenYellowRed

438.4nmFe I (blue)Violet80%

495.8nmFe ICyan60%

526.9nmFe I (green)Green100%

532.8nmFe I (green)Green70%

Dominant line 526.9 nmRange 438–533 nmTransitions 4