26FeIron55.845 u
Iron (Fe)
Iron is a transition metal with atomic number 26, in period 4 and group 8 of the periodic table. Its atomic mass is 55.845 u and its electron configuration is [Ar] 3d⁶ 4s². Solid at 25 °C.
Key facts
| Atomic number | 26 |
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| Atomic mass | 55.845 u |
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| Category | Transition Metal |
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| Period | 4 |
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| Group | 8 |
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| Block | d |
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| Electron configuration | [Ar] 3d⁶ 4s² |
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| Electrons per shell | 2, 8, 14, 2 |
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| Electronegativity (Pauling) | 1.83 |
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| Oxidation states | −2, −1, +1, +2, +3, +4, +5, +6, +7common in bold |
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| State at 25 °C | Solid |
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| Melting point | 1811 K1537.85 °C |
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| Boiling point | 3134 K2860.85 °C |
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| Density | 7.874 g/cm³ |
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Atomic properties
| First ionization energy | 7.902 eV |
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| Electron affinity | 15.7 kJ/mol |
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| Atomic radius | 126 pm |
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| Covalent radius | 132 pm |
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| Van der Waals radius | 194 pm |
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| Common ions | Fe³⁺, Fe²⁺ |
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| Protons, neutrons, electrons | 26, 30, 26 |
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Physical and thermal properties
| Molar volume | 7.09 cm³/mol |
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| Heat of fusion | 13.8 kJ/mol |
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| Heat of vaporization | 347 kJ/mol |
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| Specific heat | 449 J/(kg·K) |
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| Thermal conductivity | 79 W/(m·K) |
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| Thermal expansion | 1.18 × 10⁻⁵ K⁻¹ |
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| Mohs hardness | 4 |
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| Young’s modulus | 211 GPa |
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| Crystal structure | Body-centered cubic |
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| Magnetic type | Ferromagnetic |
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Identification and history
| CAS number | 7439-89-6 |
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| Latin name | Ferrum |
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| Discovered by | Known since antiquity |
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| Named by | --- |
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Natural isotopes
| Isotope | Mass (u) | Abundance |
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| 54Fe | 53.939608 | 5.845 % |
| 56Fe | 55.934936 | 91.754 % |
| 57Fe | 56.935392 | 2.119 % |
| 58Fe | 57.933274 | 0.282 % |
Data checked against PubChem (NIH), IUPAC, the NIST Atomic Spectra Database and the IAEA (NUBASE and AME), the same data you see in the app.
A dash (---) means there is no reliable published measurement. The app never makes one up.
See Iron in the app
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Periodic Table