Iridium (Ir)
Transition metal
Iridium is the most corrosion-resistant metal known and nearly ties osmium as the densest. A worldwide iridium-rich clay layer is the smoking gun for the asteroid impact that ended the dinosaurs.
Position on the periodic table
Atomic properties
| Atomic number | 77 |
|---|---|
| Atomic mass | 192.217 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d7 |
| Noble gas shorthand | [Xe] 4f14 5d7 6s2 |
| Electrons per shell | 2, 8, 18, 32, 15, 2 |
| Valence electrons (outer shell) | 2 |
| Common oxidation states | +4, +3 |
| Electronegativity (Pauling) | 2.2 |
| Covalent radius (approx.) | 141 pm |
| First ionization energy | 880 kJ/mol |
| Electron affinity | 150.9 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 22.56 g/cm³ |
| Melting point | 2445.8 °C (2719 K) |
| Boiling point | 4129.9 °C (4403 K) |
| Appearance | silvery white |
| Radioactive | No |
| Origin | Occurs naturally |
Electron configuration of iridium
Iridium's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d7, usually shortened to [Xe] 4f14 5d7 6s2. Its electrons occupy 6 shells (2, 8, 18, 32, 15, 2), placing it in period 6 of the d-block. Explore it interactively in the electron configuration calculator.
Uses of iridium
- Spark plug electrodes
- Crucibles for growing high-purity crystals
- Electrodes for chlorine production
- Deep-water and satellite components
Biological role: None known.
Occurrence: Among the rarest elements in the crust; concentrated in meteorites.
Common compounds of iridium
IrCl3
Iridium(III) chloride
History and discovery
Discovered: 1803 — Smithson Tennant. Name origin: From Iris, Greek goddess of the rainbow, for its colourful salts.
Smithson Tennant identified iridium in 1803; a platinum-iridium bar defined the kilogram for over a century.
Safety notes
Inert and safe in bulk form.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Iridium
1. What is the chemical symbol of Iridium?
2. What is the atomic number of Iridium?
3. Which category does Iridium belong to?
4. What is the state of Iridium at room temperature?
5. Which period of the periodic table is Iridium in?
Iridium FAQs
What is the atomic number of iridium?
Iridium's atomic number is 77 — every iridium atom has 77 protons in its nucleus.
What is the symbol for iridium?
Ir. From Iris, Greek goddess of the rainbow, for its colourful salts.
Is iridium a metal, nonmetal, or metalloid?
Iridium is classified as a transition metal.
What state is iridium at room temperature?
At about 25 °C, iridium is a solid. It melts at 2445.8 °C.
What is iridium used for?
Key uses include: spark plug electrodes; crucibles for growing high-purity crystals; electrodes for chlorine production.
Related elements
Keep working with this element
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