Cobalt (Co) – element 27
Cobalt is a chemical element with the symbol Co and atomic number 27. It is a transition metal in group 9, period 4 of the periodic table (d-block), and is a solid at room temperature.
Cobalt (Co) has atomic number 27, atomic mass 58.933 u and electron configuration [Ar] 3d7 4s2.
Cobalt facts
| Symbol | Co |
|---|---|
| Atomic number | 27 |
| Atomic mass | 58.933 u (g/mol) |
| Category | transition metal |
| Group | group 9 |
| Period | 4 |
| Block | d-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d7 |
| Noble-gas notation | [Ar] 3d7 4s2 |
| Electrons per shell | 2, 8, 15, 2 |
Bohr model and shells
Cobalt has 27 electrons in 4 shells: 2, 8, 15, 2. Full configuration and noble-gas notation are in the table; work out any element or ion with the electron configuration calculator.
Physical and atomic properties
| Melting point | 1768 K (1494.8 °C) |
|---|---|
| Boiling point | 3200 K (2926.8 °C) |
| Density | 8.9 g/cm³ |
| Electronegativity (Pauling) | 1.88 |
| Electron affinity | 63.898 kJ/mol |
| Ionization energies | 760.4, 1648, 3232 kJ/mol (1st, 2nd, 3rd) |
| Molar heat capacity | 24.81 J/(mol·K) |
| Discovered by | Georg Brandt |
Use the atomic mass in the molar mass calculator for any formula containing Co.
Position in the periodic table
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Frequently asked questions
What is the atomic mass of cobalt?
The atomic mass of cobalt is 58.933 u, so one mole of cobalt atoms weighs 58.933 g.
What is the electron configuration of cobalt?
Cobalt has 27 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁷, or [Ar] 3d⁷ 4s² in noble-gas notation. Electrons per shell: 2, 8, 15, 2.
Is cobalt a metal?
Yes. Cobalt is a transition metal.
Where is cobalt on the periodic table?
Cobalt is in group 9, period 4, in the d-block.
Data: Periodic-Table-JSON (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.