Average mass of an atom in unified atomic mass units (1 u is 1/12 of the mass of a carbon-12 atom). Accounts for the natural mix of the element’s isotopes.
Number of the vertical column, 1 to 18 in IUPAC numbering. Elements in a group share the same outer-shell layout, so their properties are alike.
Number of the horizontal row. Usually equal to the number of electron shells in the atom; palladium is the exception, with four shells in period 5.
The subshell (s, p, d or f) that receives the last electrons in the usual filling order; it divides the table into four blocks. Real atoms sometimes differ: lanthanum starts the f-block but has no f electrons.
[Xe] 6s² 4f¹⁴ 5d⁷
How electrons are arranged in subshells. The bracket stands for the previous noble gas; the superscript is the number of electrons in a subshell.
2, 8, 18, 32, 15, 2
Number of electrons in each shell, from the nucleus outwards.
2,446 °C (2,719 K)
Temperature at which the solid turns liquid at standard pressure. Helium, carbon and arsenic do not melt at normal pressure: helium needs about 25 atm, carbon and arsenic turn straight into vapour.
4,428 °C (4,701 K)
Temperature at which the liquid boils at standard pressure. For carbon and arsenic, the temperature at which the solid turns straight into vapour (sublimation).
22.42 g/cm³
Mass of one cubic centimetre of the substance. For gases, at 0 °C and standard pressure.
2.20 Pauling
How strongly an atom pulls electrons towards itself in a chemical bond. On the Pauling scale it runs from 0.79 for caesium to 3.98 for fluorine.
8.967 eV
Energy needed to remove the most loosely bound electron from an atom. The lower it is, the more easily the element gives up an electron, which is typical of metals.
1.564 eV
Energy released when a neutral atom gains an electron. Highest for the halogens. Noble gases, nitrogen and some metals form no stable negative ion.
141 pm
Half the length of a single covalent bond between two atoms of the element. It shows the size of an atom inside a molecule or crystal: 76 pm for carbon, 132 pm for iron.
+4, +3
Charges the atom would have in its compounds if all its bonds were ionic; the main ones are listed.
Iridium (Ir) is a chemical element with atomic number 77. It sits in group 9 and period 6 of the periodic table, in the d-block. It is a transition metal. At room temperature it is a solid. Its standard atomic weight is 192.22.
Origin of the name
Iridium is named after Iris, the Greek goddess of the rainbow, because its salts come in so many colours. Smithson Tennant discovered it in 1803, together with osmium, in the black residue left after platinum ore had been dissolved in aqua regia.
Where is iridium found?
Iridium is obtained from platinum ores and as a by-product of nickel mining.
What is iridium used for?
Iridium is the most corrosion-resistant metal known. It hardens platinum, and their alloys make crucibles and other equipment for very high temperatures, as well as the tips of long-life spark plugs. The old international standard metre was a bar of platinum with 10% iridium.
Interesting facts
All over the world, rocks from the end of the age of the dinosaurs contain a thin layer rich in iridium. Asteroids contain far more iridium than the Earth’s crust, so this layer is evidence of a huge impact at that time, linked to the extinction of the dinosaurs.