Cobalt (Co)
Transition metal · d-block · period 4 · group 9
Hard, lustrous, silvery-blue magnetic metal.
Cobalt (symbol Co) is chemical element number 27, a transition metal in group 9, period 4 of the periodic table. Its standard atomic weight is 58.933 and its electron configuration is [Ar] 3d7 4s2. At room temperature it is a solid. Its compounds have coloured glass and ceramics deep blue for centuries ('cobalt blue').
Properties
| Atomic number | 27 |
|---|---|
| Atomic mass | 58.933 |
| Category | Transition metal |
| Block | d-block |
| Group · Period | 9 · 4 |
| Electron configuration | [Ar] 3d7 4s2 |
| Electrons per shell | 2, 8, 15, 2 |
| State at 25 °C | solid |
| Melting point | 1768 K |
| Boiling point | 3200 K |
| Density | 8.9 g/cm³ |
| Electronegativity (Pauling) | 1.88 |
| Radioactive | No |
| Origin | primordial |
| Discovered | 1735 · Georg Brandt |
Key facts about Cobalt
- Its compounds have coloured glass and ceramics deep blue for centuries ('cobalt blue').
- One of only three elements that are magnetic at room temperature (with iron and nickel).
- Vitamin B12 is built around a single cobalt atom.
- Cobalt is a key metal in the cathodes of most lithium-ion batteries.
What Cobalt is used for
Battery cathodes, superalloys for jet engines, blue pigments, strong permanent magnets, cutting tools.
Where it sits in the periodic table
Cobalt is in group 9, period 4, of the d-block. Its electron configuration [Ar] 3d7 4s2 means its outermost shell holds 2 electrons, which is what places it here and explains much of its chemistry. See Cobalt on the interactive table →
Cobalt — frequently asked questions
What is Cobalt used for?
Battery cathodes, superalloys for jet engines, blue pigments, strong permanent magnets, cutting tools.
Is Cobalt radioactive?
No. Cobalt has at least one stable isotope and is not radioactive.
What is the electron configuration of Cobalt?
Cobalt has the electron configuration [Ar] 3d7 4s2, which is 2, 8, 15, 2 electrons per shell.
What group and period is Cobalt in?
Cobalt is in group 9, period 4, in the d-block. Its outer shell holds 2 electrons.
Who discovered Cobalt?
Cobalt was discovered in 1735 by Georg Brandt.