Iridium
Definition and meaning of Iridium in chemistry.
Iridium is a chemical element with the symbol Ir and atomic number 77, known as the most corrosion-resistant metal on the periodic table. It is a very hard, brittle, silvery-white transition metal of the platinum group, ranking as the second-densest naturally occurring element.
In more detail
Located in group 9 of the periodic table, iridium is found in meteorites in much higher abundances than in the Earth's crust, making it a key indicator of extraterrestrial impacts, such as the Cretaceous-Paleogene extinction event. The metal exhibits extraordinary physical properties, including a remarkably high melting point and unparalleled resistance to corrosion, remaining entirely unattacked by any single acid, including aqua regia, at room temperature. Chemically, it forms compounds mostly in the +3 and +4 oxidation states, though it can exhibit states ranging from -3 to +9, the latter being the highest known oxidation state for any element, observed in the [IrO4]+ cation. Iridium is generally extracted as a byproduct of nickel and copper mining, where it is found concentrated alongside other platinum-group metals in sulfide ores. Its extreme hardness and brittleness make it incredibly difficult to machine, form, or work into shape, requiring specialized high-temperature metallurgy techniques.
Key facts
| Field | General Chemistry |
|---|---|
| Symbol | Ir |
| Atomic number | 77 |
| Atomic mass | 192.22 u |
| Category | Transition Metal |
| Density near room temperature | 22.56 grams per cubic centimeter |
| Melting point | 2446 degrees Celsius |
| Year discovered | 1803 by Smithson Tennant |
Iridium is widely utilized in the manufacturing of high-performance spark plugs, where its exceptional resistance to heat and wear ensures long-lasting electrical ignition under extreme engine conditions.
Frequently asked questions
Why is iridium so rare in the Earth's crust?
During the early molten stage of Earth's formation, dense iron-loving elements like iridium sank toward the planetary core, leaving the outer crust severely depleted of these metals.
How does iridium prove asteroid impacts?
Because iridium is rare on Earth but relatively common in certain asteroids, a distinct geological layer enriched with iridium indicates that a massive extraterrestrial body impacted the planet and spread the material globally.