Iridium (Ir)

Iridium properties

Atomic number

77

Atomic mass

192.22 u

Category

Transition metal

Group

9

Period

6

Block

d-block

State at room temp.

Solid

Electronegativity

2.2

Melting point

2,719 K (2,445.8 °C)

Boiling point

4,403 K (4,129.8 °C)

Density

22.56 g/cm³

Valence electrons

2

Common charges

+3, +4

Oxidation states

+4, +3

Atomic radius

202 pm

Ionization energy

9.1 eV

Electron affinity

1.565 eV

Radioactive

No, has stable isotopes

Discovered

1803

Iridium electron configuration

The electron configuration of Iridium (Ir) is [Xe] 4f14 5d7 6s2. Its 77 electrons are arranged in shells as 2, 8, 18, 32, 15, 2.

Protons, neutrons and electrons in Iridium

A neutral Iridium atom has 77 protons and 77 electrons. Most Iridium atoms have about 115 neutrons: the atomic mass rounded to 192, minus the atomic number 77.

Neutrons are approximate: atoms of the same element can have different numbers of neutrons (isotopes). Atomic number and mass

How many valence electrons does Iridium have?

2

Iridium has 2 valence electrons, counting the electrons in its outermost s subshell. Like most transition metals, it can also use d electrons in bonding.

See every element: Periodic table with valence electrons

Iridium orbital diagram

Each box is an orbital that holds up to two electrons with opposite spins (↑↓). The inner shells are the same as the noble gas in brackets. How to write electron configurations

Molar mass of Iridium

192.22 g/mol

One mole of Iridium atoms (6.022 × 10²³ atoms) has a mass of 192.22 grams. Use this value to convert between grams and moles.

Iridium facts

• Iridium is considered the most corrosion-resistant metal and is not attacked by any acid, even aqua regia, at normal temperatures.
• A thin, iridium-rich layer in rocks about 66 million years old supports the idea that an asteroid impact helped wipe out the dinosaurs.
• Iridium (Ir) has atomic number 77 and is a solid at room temperature. It was discovered in 1803.

Position in the periodic table

Iridium is element 77, in period 6 and group 9 of the periodic table, in the d-block.

All transition metals

Uses of Iridium

Iridium is used for the electrode tips of long-life spark plugs and for crucibles that hold molten material while crystals are grown for electronics. Iridium oxide coatings are used on electrodes in water electrolyzers that produce hydrogen. Radioactive iridium-192 is used to check welds and pipes for hidden flaws and to treat some cancers from inside the body.

Who discovered Iridium?

English chemist Smithson Tennant discovered iridium in 1803 in London, in the insoluble residue left after dissolving platinum ore in aqua regia. He named it after Iris, the Greek goddess of the rainbow, because its salts have so many colors.

Where does the name come from?

Iridium comes from the Greek iris, meaning 'rainbow', which was also the name of the Greek goddess of the rainbow. Smithson Tennant chose it in 1803 because the salts of the metal display a wide range of colors.

Discovery timeline