Iridium
Iridium is a chemical element with the symbol Ir and atomic number 77. It is a very hard, brittle, silvery-white transition metal of the platinum group, considered the second-densest naturally occurring metal after osmium, with a density of 22.56 g/cm³. Its name, derived from the Greek word 'iris' (rainbow), refers to the various colors of its compounds.
- symbol
- Ir
- atomic_number
- 77
- discovered_by
- Smithson Tennant
- density
- 22.56 g/cm³
- natural_isotopes
- 191Ir and 193Ir
- key_property
- most corrosion-resistant metal
Lore & Background
The element's name, derived from the Greek word 'iris' (rainbow), reflects the varied colors of its compounds. It is found in meteorites in much higher abundance than in the Earth's crust, and its unusually high abundance in the clay layer at the Cretaceous–Paleogene boundary gave rise to the Alvarez hypothesis that a massive extraterrestrial impact caused the extinction of non-avian dinosaurs 66 million years ago, now known to be produced by the impact that formed the Chicxulub crater. Similarly, an iridium anomaly in core samples from the Pacific Ocean suggested the Eltanin impact of about 2.5 million years ago.
Reader's Guide
Iridium is significant for its extreme physical and chemical properties. Its high density (22.56 g/cm³) is only slightly lower than that of osmium, and it has the second-highest modulus of elasticity among metals. These properties make iridium valuable in high-performance spark plugs, crucibles for semiconductor recrystallization, and electrodes for chlorine production. Its isotopes have practical applications: 192Ir is used in brachytherapy and industrial radiography, while 191Ir was the first isotope to show a Mössbauer effect, useful in spectroscopy. The element's presence in meteorites and the Cretaceous–Paleogene boundary layer provided key evidence for the asteroid impact hypothesis of dinosaur extinction. Despite its high cost and difficulty in fabrication due to brittleness, iridium remains essential in extreme conditions where corrosion resistance and mechanical strength are critical.
Did You Know?
- Iridium is the second-densest naturally occurring metal, with a density of 22.56 g/cm³, only slightly less than osmium.
- The unusually high abundance of iridium in the clay layer at the Cretaceous–Paleogene boundary supported the Alvarez hypothesis that an asteroid impact caused dinosaur extinction.
- Iridium is the most corrosion-resistant metal known, not attacked by acids including aqua regia.
- The isotope 192Ir, with a half-life of 73.82 days, is used in brachytherapy and industrial radiography for nondestructive testing of welds.
Frequently Asked Questions
What exactly is Iridium in the periodic table?
Iridium (symbol Ir, atomic number 77) is a silvery-white, hard, and brittle transition metal belonging to the platinum group. It sits among the densest naturally occurring metals, trailing only osmium in density at 22.56 g/cm³.
What does the name Iridium actually mean?
The name comes from the Greek word 'iris,' meaning rainbow, a nod to the striking variety of colors that iridium compounds can display. Tennant chose it to capture the visual diversity of the element's chemistry.
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