Iridium (Ir)
Element 77 · Transition metal · Solid at 25 °C · Group 9, Period 6
Iridium is the most corrosion-resistant metal known. A thin iridium-rich layer in Earth's rocks marks the asteroid impact tied to the dinosaurs' extinction.
On the periodic table, iridium sits in group 9 in period 6. It is one of 38 elements classified as a transition metal, and at room temperature (25 °C) it is a solid.
Transition metals occupy the wide d-block in the middle of the table. As a family they are hard, dense, high-melting metals that conduct heat and electricity well. Their partly filled d-orbitals let many of them take several oxidation states, form vividly colored compounds, and act as catalysts — which is why so much of industry, and so much of biology, runs on this block.
Properties of iridium
| Atomic number (Z) | 77 |
|---|---|
| Symbol | Ir |
| Atomic mass | 192.22 |
| Category | Transition metal |
| Group | 9 |
| Period | 6 |
| Block | d-block |
| Metal / nonmetal | Metal |
| State at 25 °C | Solid |
| Electron configuration | [Xe] 4f14 5d7 6s2 |
| Electronegativity (Pauling) | 2.2 |
| Melting point | 2,446 °C (2,719.15 K / 4,434.8 °F) |
| Boiling point | 4,428 °C (4,701.15 K / 8,002.4 °F) |
| Density | 22.56 g/cm³ |
Position in the periodic table
Iridium shares group 9 with Cobalt (Co), Rhodium (Rh), Meitnerium (Mt). Elements in the same group have the same number of outer electrons, so they tend to behave alike chemically — comparing them is one of the fastest ways to see periodic trends in action.
Within this dataset, it has the #2 highest measured density of the 97 elements with recorded values; its melting point is the #8 highest of the 102 elements with measured melting points.
Physical properties
Iridium melts at 2,446 °C (2,719.15 K / 4,434.8 °F) and boils at 4,428 °C (4,701.15 K / 8,002.4 °F), giving it a liquid range of about 1,982 °C at standard pressure.
Its density is 22.56 g/cm³.
See also: the interactive periodic table, how to read the periodic table, periodic trends.