Nepedia
Back to Discover
Advanced Reader
⚛️

Iridium

physical science Maturity 7-9 Next article →

Iridium is a chemical element with the symbol Ir and atomic number 77. It is a member of the platinum group metals. This metal is silvery-white with a slight yellowish cast.

iridium2
iridium2

Iridium is considered the second-densest naturally occurring metal. Only osmium is denser than iridium. X-ray crystallography shows that iridium has a density of 22.56 grams per cubic centimeter. This makes it incredibly heavy for its size. It is also one of the most corrosion-resistant metals known to science.

Elemental abundances
Elemental abundances

The physical properties of iridium make it very difficult to work with. It is extremely hard and very brittle. This means it can snap or shatter rather than bending under pressure. Because of this brittleness, solid iridium is hard to machine or form. Instead, engineers often use powder metallurgy to create iridium parts.

iridium2
iridium2

Iridium has a very high melting point. It is the only metal that maintains good mechanical properties in air at temperatures above 2000 degrees Celsius. It also has the 10th highest boiling point of all elements. Its stiffness is also notable, as it has the second-highest modulus of elasticity among metals.

Iridium has two stable isotopes found in nature: 191Ir and 193Ir. The 193Ir isotope is the more abundant of the two. These two isotopes make up 100% of the stable iridium found on Earth. There are also 40 known radioisotopes of iridium. One specific isotope, 192Ir, is very useful in industry. It has a half-life of 73.82 days. Scientists use it in brachytherapy to treat medical issues. It is also used in industrial radiography to test welds in steel pipes.

IrCl3(aq)x
IrCl3(aq)x

Chemistry involving iridium is very complex and diverse. The element can form compounds in many different oxidation states. These states range from -3 all the way up to +9. The +9 state is actually the highest recorded for any element. Most common oxidation states are +1, +2, +3, and +4. Iridium forms many different types of compounds, including chlorides and iodides. These are often used as industrial catalysts.

IrCl3(aq)x
IrCl3(aq)x

Iridium also plays a role in organoiridium chemistry. This involves creating bonds between iridium and carbon atoms. This field of study helps scientists understand how to activate unreactive hydrocarbons.

The history of iridium is tied to the discovery of platinum. In 1557, the Italian humanist Julius Caesar Scaliger wrote about a metal that no fire could melt. For a long time, the Spanish viewed platinum as an impurity in gold. They even made laws to prevent people from mixing them. In 1735, Antonio de Ulloa and Jorge Juan y Santacilia observed Native Americans mining platinum.

Almirante Antonio de Ulloa
Almirante Antonio de Ulloa

Later, in 1803, the British chemist Smithson Tennant discovered iridium. He found it in the residues of platinum ores that would not dissolve in acid. The name iridium comes from the Greek word iris, meaning rainbow.

Winged goddess Cdm Paris 392
Winged goddess Cdm Paris 392

This refers to the many colors its compounds can produce.

Iridium is a very rare element in the Earth's crust. In 2023, the estimated annual production was only 7 tonnes. Despite its rarity, iridium is essential for modern technology. It is used in high-performance spark plugs for engines. It is also used in crucibles for recrystallizing semiconductors at high temperatures.

IrCl3(aq)x
IrCl3(aq)x

Additionally, iridium is a component in some organic light-emitting diodes, or OLEDs. It is also used as electrodes in the chloralkali process to produce chlorine.

One of the most famous uses of iridium is in studying Earth's history. Iridium is found in much higher amounts in meteorites than in the Earth's crust.

Willamette Meteorite AMNH
Willamette Meteorite AMNH

Scientists found an unusually high amount of iridium in a clay layer from the Cretaceous–Paleogene boundary. This discovery led to the Alvarez hypothesis. This hypothesis suggests that a massive extraterrestrial object hit Earth about 66 million years ago. This impact caused the extinction of the non-avian dinosaurs.

K-T boundary
K-T boundary

A similar iridium anomaly was found in the Pacific Ocean, suggesting another impact occurred about 2.5 million years ago.

656 words

Where will your curiosity go next?

Keep exploring at your chosen reading level.

🖼️ Images & Media (12)
File:iridium2.jpg
iridium2.jpg
File:IrCl3(aq)x.jpg
IrCl3(aq)x.jpg
File:Ir2Cl2 cod 2improved.svg
Ir2Cl2 cod 2improved.svg
File:C-HactnBergGrah.png
C-HactnBergGrah.png
File:Winged goddess Cdm Paris 392.jpg
Winged goddess Cdm Paris 392.jpg
File:Platinum symbol.svg
Platinum symbol.svg
File:Almirante Antonio de Ulloa.jpg
Almirante Antonio de Ulloa.jpg
File:Elemental abundances.svg
Elemental abundances.svg
File:Willamette Meteorite AMNH.jpg
Willamette Meteorite AMNH.jpg
File:K-T boundary.jpg
K-T boundary.jpg
File:Platinum-Iridium meter bar.jpg
Platinum-Iridium meter bar.jpg
File:Gama Supreme Flat Top ebonite eyedropper fountain pen 3.JPG
Gama Supreme Flat Top ebonite eyedropper...
More to explore

✨ What else?

Related topics you might enjoy

🔬 Go deeper

More advanced topics to explore

🪜 Step back

Simpler topics to build understanding

What is Nepedia?

A free, ad-free encyclopedia for children. Every article is written at five reading levels, so the same page works for a five-year-old and a fifteen-year-old — use the level switcher above to see this one change. No account needed to read.