Cobalt (Co)
Cobalt is element 27, a transition metal in period 4, group 9 of the periodic table. At room temperature it is a solid.
Electron configuration [Ar] 3d7 4s2
Electrons per shell 2, 8, 15, 2
Cobalt data
| Atomic number | 27 |
|---|---|
| Symbol | Co |
| Atomic mass | 58.933 u |
| Category | Transition metal |
| Group | 9 |
| Period | 4 |
| Block | d |
| State at 25 °C | solid |
| Melting point | 1768 K (1494.9 °C) |
| Boiling point | 3200 K (2926.9 °C) |
| Density | 8.9 g/cm³ |
| Electronegativity (Pauling) | 1.88 |
| Atomic radius | 126 pm |
| 1st ionization energy | 760 kJ/mol |
| Electron affinity | -64 kJ/mol |
| Oxidation states | -1, +1, +2, +3, +4, +5 |
| Common ion charge | 2+, 3+ |
| Discovered | Known since antiquity |
Orbital diagram
Each box is one orbital holding up to two electrons of opposite spin. Following Hund’s rule, electrons spread out singly across a subshell before pairing.
Work through cobalt’s configuration and its ions →
Where cobalt sits
Cobalt belongs to the transition metals. Its Pauling electronegativity of 1.88 is mid-range; see the electronegativity chart and periodic trends for context. To use its mass in a calculation, try the molar mass calculator.
Cobalt FAQ
What is the electron configuration of cobalt?
Cobalt (Z = 27) has the configuration 1s2 2s2 2p6 3s2 3p6 3d7 4s2. In noble-gas shorthand that is [Ar] 3d7 4s2.
How many valence electrons does cobalt have?
9 (2 outer s + 7 d electrons; 2 in the outermost shell).
What is the atomic mass of cobalt?
The standard atomic weight of cobalt is 58.933 u, so one mole weighs 58.933 g.
Is cobalt a metal?
Yes. Cobalt is a transition metal.
What is the charge of a cobalt ion?
Cobalt most commonly forms Co2+ or Co3+.