Cobalt

Cobalt is a chemical element with the symbol Co and atomic number 27. Like nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron.

What the numbers say

At standard temperature and pressure Cobalt is a solid, sitting in period 4, group 9 of the d-block.

Its melting point of 1768 K (1495 °C) is the 31st highest of the 110 elements with a measured value — mid-range among the elements.

At 8.9 g/cm³ it is the 35th densest of 96 elements with a quoted density.

Pauling electronegativity is 1.88. Paired with oxygen (3.44) that is a difference of 1.56, which puts the bond polar covalent — oxides here tend to be semiconducting or refractory rather than salt-like.

In the solid state it takes a simple hexagonal structure — hexagonal packing offers few easy slip systems, so properties are anisotropic and formability is limited.

It is reported in 6 oxidation states (-1, 1, 2, 3, 4, 5), which sets how many distinct compounds and phases it can form.

First identified in 1735.

Crystal structure

Check it against computed structures

The structure search queries the Materials Project, OQMD and the Open Materials Database for computed crystal structures containing Co — with DFT formation energy, hull stability and band gap where the provider publishes them.