Iridium
Definition and meaning of Iridium in chemistry.
![Iridium element card: symbol Ir, atomic number 77, atomic mass 192.22, electron configuration [Xe] 4f¹⁴ 5d⁷ 6s², oxidation states +4 +3, Transition metal, group 9, period 6, solid at room temperature.](/assets/images/terms/iridium-chemical-element.webp)
Iridium is a chemical element with the symbol Ir and atomic number 77. It is the most corrosion-resistant metal on the entire periodic table. This silvery-white transition metal is very hard, extremely brittle, and ranks as the second-densest natural element on Earth.
In more detail
Iridium sits in group 9 of the periodic table as a heavy transition metal. It is much more common in space rocks than in the outer crust of our planet. When the early Earth was hot and molten, heavy metals like iridium sank into the deep core.
Students often think iridium is rare everywhere, but it is actually abundant in Earth's core. High levels of this metal in rock layers point to past asteroid impacts. One famous impact released enough iridium dust to cause the dinosaur extinction.
Iridium resists rust and decay much better than any other metal on Earth. No single acid can dissolve this stubborn metal at room temperature. Even a very strong acid mixture called aqua regia cannot dissolve solid iridium.
In chemical compounds, iridium mostly takes plus 3 and plus 4 oxidation states. An oxidation state shows how many electrons an atom shares or transfers. It can even reach a plus 9 state in the [IrO4]+ cation.
A cation is a positively charged ion that forms during chemical reactions. This rare cation represents the highest known oxidation state for any element. Miners extract iridium as a byproduct of nickel and copper mining.
They find it mixed inside sulfide ores alongside other metals like platinum. Its extreme hardness and brittle nature make it very difficult to shape. Workers must use special high-temperature methods to mold this metal.
Key facts
| Field | General Chemistry |
|---|---|
| Symbol | Ir |
| Atomic number | 77 |
| Atomic mass | 192.22 u |
| Category | Transition-Metal |
| Density | 22.56 grams per cubic centimeter |
| Melting point | 2446 degrees Celsius |
Manufacturers use iridium to make high-performance spark plugs for heavy machinery. Its extreme resistance to heat and wear makes it perfect for this tough job. These spark plugs provide reliable electrical sparks inside hot and demanding car engines. The durable metal lasts a very long time before it finally wears out.
Frequently asked questions
Why is iridium so rare in the Earth's crust?
During early planetary formation, the Earth was a hot and molten liquid. Heavy metals like iridium sank deep down toward the center of the planet. This process left the outer crust with very tiny amounts of these metals.
How does iridium prove asteroid impacts?
Iridium is rare on Earth but remains very common in space rocks. A distinct rock layer full of iridium shows that a massive asteroid hit the planet. The violent crash spread this metallic space dust all over the globe.
Can aqua regia dissolve iridium metal at room temperature?
No, aqua regia cannot dissolve iridium at room temperature because the metal is extremely stable. Only very high temperatures and pressures can force the acid to react with it.
Related terms
Sources & references
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