Cobalt (Co): electron configuration, atomic mass and facts
Cobalt (Co) is element 27 of the periodic table, a transition metal in period 4, group 9. Its electron configuration is [Ar] 3d7 4s2, with electrons arranged in shells 2, 8, 15, 2, and its standard atomic weight is 58.933 u.
▶ Watch Cobalt’s electrons orbit in the interactive periodic tableCobalt at a glance
| Symbol | Co |
|---|---|
| Atomic number | 27 |
| Atomic mass | 58.933 u |
| Category | Transition metal |
| Group | 9 |
| Period | 4 |
| Block | d-block |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d7 4s2 |
| Noble-gas shorthand | [Ar] 3d7 4s2 |
| Electrons per shell | 2, 8, 15, 2 |
| Electronegativity (Pauling) | 1.88 |
| State at 20 °C | solid |
Where is Cobalt on the periodic table?
Cobalt is in period 4, group 9, in the d-block. The period number matches its 4 electron shells, and the block names the subshell its last electrons fill. In the same group, Rhodium sits directly below it. Elements in the same column of the d-block often have similar chemistry.
How to work out the electron configuration of Cobalt
Put 27 electrons into subshells in order of rising energy, filling each before starting the next: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁶ (18), 4s² (20), 3d⁷ (27). In shorthand, [Ar] stands for the 18 electrons of argon, giving [Ar] 3d⁷ 4s².
How electronegative is Cobalt?
Cobalt has a Pauling electronegativity of 1.88, ranking 41 of the 100 elements with a known value (fluorine is highest at 3.98). That is in the middle of the range.
Frequently asked questions
What is the electron configuration of Cobalt?
The electron configuration of Cobalt (Co) is 1s2 2s2 2p6 3s2 3p6 3d7 4s2. In noble-gas shorthand it is written [Ar] 3d7 4s2.
How many electrons does Cobalt have in each shell?
Cobalt has 27 electrons arranged in shells as 2, 8, 15, 2.
What is the atomic mass of Cobalt?
The standard atomic weight of Cobalt is 58.933 u, so one mole of Cobalt atoms has a mass of about 58.933 g.
Is Cobalt a metal?
Yes. Cobalt is a transition metal.
Explore nearby elements
More transition metals: Chromium, Manganese, Iron, Nickel, Copper, Zinc. See all elements on the periodic table.