Element: Iron
General data
| Element name | Iron |
|---|---|
| Chemical symbol | Fe |
| Atomic number Z | 26 |
| Year discovered | known since antiquity |
| Standard state (25°C) | Solid |
| Category | Transition metal |
| Block | d |
| Atomic mass | 55.845 |
| CPK color | #E06633 |
Physical properties
| Melting point | 1811 K (1538 °C) |
|---|---|
| Boiling point | 3134 K (2861 °C) |
| Density | 7.874 g/cm³ |
Energy properties
| First ionization energy | 7.902 eV |
|---|---|
| Electron affinity | 0.163 eV |
Atomic structure
| Protons | 26 (Atomic number) |
|---|---|
| Neutrons (Fe-56, most abundant isotope) | 30 |
| Electrons | 26 |
| Electron configuration | [Ar] 4s² 3d⁶ |
| Oxidation states | +3, +2 |
| Electronegativity (Pauling) | 1.83 |
| Atomic radius (van der Waals) | 194 pm |
Ionization energies - NIST ASD (26 states)
| State | Charge | Ioniz. energy (eV) | Type |
|---|---|---|---|
| Fe I | 0+ | 7.9024681 ± 0.0000012 | measured |
| Fe II | 1+ | 16.19921 ± 0.00005 | measured |
| Fe III | 2+ | 30.651 ± 0.012 | measured |
| Fe IV | 3+ | 54.91 ± 0.04 | measured |
| Fe V | 4+ | 75 ± 0.15 | semi-empirical |
| Fe VI | 5+ | 98.985 ± 0.015 | measured |
| Fe VII | 6+ | 124.9671 ± 0.0025 | measured |
| Fe VIII | 7+ | 151.06 ± 0.012 | measured |
| Fe IX | 8+ | 233.6 ± 0.4 | semi-empirical |
| Fe X | 9+ | 262.1 ± 0.12 | semi-empirical |
| Fe XI | 10+ | 290.9 ± 0.4 | semi-empirical |
| Fe XII | 11+ | 330.8 ± 0.6 | semi-empirical |
| Fe XIII | 12+ | 361 ± 0.7 | semi-empirical |
| Fe XIV | 13+ | 392.2 ± 0.7 | semi-empirical |
| Fe XV | 14+ | 456.2 ± 0.5 | measured |
| Fe XVI | 15+ | 489.312 ± 0.014 | semi-empirical |
| Fe XVII | 16+ | 1262.7 ± 0.7 | semi-empirical |
| Fe XVIII | 17+ | 1357.8 ± 1.9 | semi-empirical |
| Fe XIX | 18+ | 1460 ± 3 | semi-empirical |
| Fe XX | 19+ | 1575.6 ± 0.5 | measured |
| Fe XXI | 20+ | 1687 ± 1 | semi-empirical |
| Fe XXII | 21+ | 1798.4 ± 0.8 | semi-empirical |
| Fe XXIII | 22+ | 1950.4 ± 1.8 | semi-empirical |
| Fe XXIV | 23+ | 2045.759 ± 0.007 | calculated |
| Fe XXV | 24+ | 8828.1864 ± 0.0012 | calculated |
| Fe XXVI | 25+ | 9277.6886 ± 0.0003 | calculated |
Value type as given by NIST ASD: measured - from evaluated experimental data; calculated - from ab initio calculations (mostly highly ionised atoms that have not been measured; for the simplest ones, e.g. H I, the calculation is more accurate than measurement); semi-empirical - from interpolation, extrapolation or another semi-empirical method.
Photos
Isotopes (32)
| A | N | Half-life | Decay |
|---|---|---|---|
| Fe-45 | 19 | 2.6 ms | 2p |
| Fe-46 | 20 | 13.9 ms | EC/β⁺ |
| Fe-47 | 21 | 21.9 ms | EC/β⁺ |
| Fe-48 | 22 | 45.5 ms | EC/β⁺ |
| Fe-49 | 23 | 64.7 ms | EC/β⁺ |
| Fe-50 | 24 | 152.0 ms | EC/β⁺ |
| Fe-51 | 25 | 305 ms | EC/β⁺ |
| Fe-52 | 26 | 8.273 h | EC/β⁺ |
| Fe-53 | 27 | 8.51 min | EC/β⁺ |
| Fe-54 | 28 | stable | - |
| Fe-55 | 29 | 2.7558 a | EC |
| Fe-56 | 30 | stable | - |
| Fe-57 | 31 | stable | - |
| Fe-58 | 32 | stable | - |
| Fe-59 | 33 | 44.495 d | β⁻ |
| Fe-60 | 34 | 2.61×10⁶ a | β⁻ |
| Fe-61 | 35 | 6.03 min | β⁻ |
| Fe-62 | 36 | 68 s | β⁻ |
| Fe-63 | 37 | 6.1 s | β⁻ |
| Fe-64 | 38 | 2.0 s | β⁻ |
| Fe-65 | 39 | 0.803 s | β⁻ |
| Fe-66 | 40 | 470 ms | β⁻ |
| Fe-67 | 41 | 398 ms | β⁻ |
| Fe-68 | 42 | 186 ms | β⁻ |
| Fe-69 | 43 | 162 ms | β⁻ |
| Fe-70 | 44 | 61.5 ms | β⁻ |
| Fe-71 | 45 | 34 ms | β⁻ |
| Fe-72 | 46 | 19 ms | β⁻ |
| Fe-73 | 47 | 12.9 ms | β⁻ |
| Fe-74 | 48 | 8 ms | β⁻ |
| Fe-75 | 49 | unknown | β⁻ |
| Fe-76 | 50 | unknown | β⁻ |
Data sources
- PubChem Periodic Table API - Retrieved on 29 June 2026 - licence: CC0
- IUPAC CIAAW - Abridged Standard Atomic Weights 2024 - Table version: 2024 - licence: Public domain
- NNDC Wallet Cards 2023 - Data as of 15 October 2024 - licence: Public domain
- NIST Atomic Spectra Database (ASD) - Retrieved on 29 June 2026 - licence: © U.S. Secretary of Commerce
- Images of Elements - Retrieved on 29 June 2026 - licence: CC BY 3.0