27CoCobalt58.933194 u
Cobalt (Co)
Cobalt is a transition metal with atomic number 27, in period 4 and group 9 of the periodic table. Its atomic mass is 58.933194 u and its electron configuration is [Ar] 3d⁷ 4s². Solid at 25 °C.
Key facts
| Atomic number | 27 |
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| Atomic mass | 58.933194 u |
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| Category | Transition Metal |
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| Period | 4 |
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| Group | 9 |
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| Block | d |
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| Electron configuration | [Ar] 3d⁷ 4s² |
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| Electrons per shell | 2, 8, 15, 2 |
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| Electronegativity (Pauling) | 1.88 |
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| Oxidation states | −3, −1, +1, +2, +3, +4, +5common in bold |
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| State at 25 °C | Solid |
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| Melting point | 1768 K1494.85 °C |
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| Boiling point | 3200 K2926.85 °C |
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| Density | 8.9 g/cm³ |
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Atomic properties
| First ionization energy | 7.881 eV |
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| Electron affinity | 63.7 kJ/mol |
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| Atomic radius | 125 pm |
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| Covalent radius | 126 pm |
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| Van der Waals radius | 192 pm |
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| Common ions | Co²⁺, Co³⁺ |
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| Protons, neutrons, electrons | 27, 32, 27 |
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Physical and thermal properties
| Molar volume | 6.67 cm³/mol |
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| Heat of fusion | 16.2 kJ/mol |
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| Heat of vaporization | 375 kJ/mol |
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| Specific heat | 421 J/(kg·K) |
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| Thermal conductivity | 100 W/(m·K) |
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| Thermal expansion | 1.3 × 10⁻⁵ K⁻¹ |
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| Mohs hardness | 5 |
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| Young’s modulus | 209 GPa |
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| Crystal structure | Simple hexagonal |
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| Magnetic type | Ferromagnetic |
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Identification and history
| CAS number | 7440-48-4 |
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| Latin name | Cobaltum |
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| Discovered by | Georg Brandt · 1735 |
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| Named by | --- |
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Natural isotopes
| Isotope | Mass (u) | Abundance |
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| 59Co | 58.933194 | 100 % |
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.
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Periodic Table