Iridium (Ir)
Element 77 · Transition metal · atomic mass 192.22 u · group 9, period 6
Electron shells: 2, 8, 18, 32, 15, 2
Iridium is the most corrosion-resistant metal known and survives temperatures that destroy nearly everything else. A worldwide iridium layer in the rock record marks the dinosaur extinction.
A thin iridium layer in 66-million-year-old rock worldwide is the fingerprint of the asteroid that killed the dinosaurs.
- Atomic number
- 77
- Atomic mass
- 192.22 u
- Electron configuration
- [Xe] 6s² 4f¹⁴ 5d⁷
- Group · period · block
- 9 · 6 · d
- Oxidation states
- +3, +4
- Electronegativity
- 2.2 (Pauling)
- Melting point
- 2,446 °C
- Boiling point
- 4,428 °C
- Density
- 22.42 g/cm³
- State at 20 °C
- Solid
- Appearance
- Silvery-white, brittle metal
- Discovered
- Smithson Tennant, 1803
77 protons, and 77 electrons when neutral
IUPAC standard atomic weight
Cobalt group
What Iridium is used for
- Spark plug and sparkplug electrode tips
- Crucibles for growing crystals
- Deep-space thermoelectric generator cladding
- Fountain-pen nibs and compass bearings
Atomic structure of Iridium
A neutral iridium atom has 77 protons and 77 electrons. Its most common isotope carries about 115 neutrons, which is where the mass number 192 comes from. Change the neutron count and you have a different isotope of iridium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 32, 15, 2. In orbital notation that is [Xe] 6s² 4f¹⁴ 5d⁷. As a d-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Iridium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Iridium sits in the periodic table
The d-block. Multiple stable oxidation states give them coloured compounds, catalytic ability and the strength that makes them the working metals of industry.
- Directly above: Rhodium — same group, so similar chemistry with a smaller atom.
- Directly below: Meitnerium — same group, one shell larger.
- One proton lighter: Osmium.
- One proton heavier: Platinum.
Discovery and naming
Iridium was discovered by Smithson Tennant in 1803. Its name comes from Iris, Greek goddess of the rainbow.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Iridium?
The standard atomic weight of Iridium is 192.22 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Iridium have?
Iridium has 77 protons, because the atomic number is the proton count and that is what makes an atom Iridium at all. A neutral Iridium atom has the same number of electrons, 77. The neutron count varies by isotope; the most common one has about 115, since 192 − 77 = 115.
What is the electron configuration of Iridium?
The electron configuration of Iridium is [Xe] 6s² 4f¹⁴ 5d⁷. Its electrons are arranged 2, 8, 18, 32, 15, 2 across 6 shells.
Is Iridium a metal?
Yes. Iridium is classified as a transition metal, on the metallic side of the table.
What group and period is Iridium in?
Iridium is in group 9 (the cobalt group), period 6, in the d-block. The group is its column and the period is its row.
What is the charge of Iridium?
Iridium most commonly forms a 3+ or 4+ ion. Like most transition metals it has several accessible oxidation states, so the charge depends on the compound.
What is the melting point of Iridium?
Iridium melts at 2,446 °C and boils at 4,428 °C. That puts it in the solids at everyday temperatures.
What is Iridium used for?
Spark plug and sparkplug electrode tips, Crucibles for growing crystals, Deep-space thermoelectric generator cladding, Fountain-pen nibs and compass bearings. Iridium is the most corrosion-resistant metal known and survives temperatures that destroy nearly everything else.
Who discovered Iridium, and where does its name come from?
Iridium (Ir) was discovered by Smithson Tennant in 1803. The name comes from Iris, Greek goddess of the rainbow.