ElementsWhat is iridium?
Iridium is a hard, silvery-white metal that resists corrosion better than any other. A thin layer of iridium in rocks around the world marks the time the dinosaurs died out.
What is iridium used for?
Spark plug tips, crucibles for growing crystals, and hard alloys with platinum.
Where the name comes from
From Iris, the Greek goddess of the rainbow, for its colourful salts.
Key facts
- Symbol
- Ir
- Atomic number
- 77
- Atomic mass
- 192.22 u
- Family
- Transition metal
- Period
- 6
- Group
- 9
- Block
- d
- State at room temperature
- Solid
- Melting point
- 2,446 °C (2,719 K, 4,435 °F)
- Boiling point
- 4,428 °C (4,701 K, 8,002 °F)
- Density
- 22.42 g/cm³
- Electrons per shell
- 2, 8, 18, 32, 15, 2
- Electron configuration
- [Xe]6s2 4f14 5d7
- Common oxidation states
- +4, +3
- Electronegativity (Pauling)
- 2.2
- First ionisation energy
- 9.1 eV
- Electron affinity
- 1.565 eV
- Atomic radius (van der Waals)
- 202 pm
- Discovered
- 1803
Place in the periodic table
Iridium is element number 77. It sits in period 6 (row 6) of the periodic table, in group 9 (column 9), and belongs to the d-block. Just before it comes osmium (76), and just after it comes platinum (78). In the same column, rhodium is above it and meitnerium is below it. Elements in one column tend to behave alike.
Family: Transition metals.
Physical properties
At room temperature iridium is a solid. It melts at 2,446 °C and boils at 4,428 °C, so it stays liquid over a range of 1,982 degrees. Its density is 22.42 grams per cubic centimetre, so a one-litre block would weigh about 22.42 kilograms. By density it ranks 2nd among the 96 elements with a measured value. It has the 8th highest melting point of all elements.
Inside the atom
An atom of iridium has 77 protons in its nucleus and, when neutral, 77 electrons around it. The electrons are arranged in 6 shells: 2, 8, 18, 32, 15, 2. The outermost shell holds 2 electrons. Written in full, the electron configuration is [Xe]6s2 4f14 5d7.
Its electronegativity on the Pauling scale is 2.2. This number shows how strongly an atom pulls shared electrons towards itself: fluorine, the strongest, is 3.98. Removing one electron from an atom takes 9.1 electronvolts (about 878 kilojoules per mole). One mole of iridium weighs 192.22 grams, so a single gram contains about 3.13 × 1021 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains iridium with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.