Iridium

Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, iridium is considered to be the second-densest naturally occurring metal (after osmium) with a density of 22.56 g/cm3 as defined by experimental X-ray crystallography.

What the numbers say

At standard temperature and pressure Iridium is a solid, sitting in period 6, group 9 of the d-block.

Its melting point of 2719 K (2446 °C) is the 8th highest of the 110 elements with a measured value — one of the most refractory elements there is.

At 22.56 g/cm³ it is the 2nd densest of 96 elements with a quoted density.

Pauling electronegativity is 2.2. Paired with oxygen (3.44) that is a difference of 1.24, 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 face-centered cubic structure — FCC packing gives 12 independent slip systems, which is why FCC metals are the ductile, formable ones.

It is reported in 10 oxidation states (-3, -1, 1, 2, 3, 4, 5, 6, 7, 8), which sets how many distinct compounds and phases it can form.

First identified in 1803.

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 Ir — with DFT formation energy, hull stability and band gap where the provider publishes them.