What Is Iridium?
Iridium, symbol Ir and atomic number 77, belongs to the transition metals — the wide central block known for hardness and multiple oxidation states.
The most corrosion-resistant metal known. A thin layer of iridium in rock proved the asteroid impact that killed the dinosaurs.
As a transition metal in Period 6 and Group 9 (Transition Metals), iridium's placement on the table reflects its electron configuration of [Xe] 4f¹⁴ 5d⁷ 6s², which governs its bonding behavior and the type of compounds it typically forms.
Position on the Periodic Table
Iridium is located in Period 6, an unusually long row that includes the entire lanthanide series.
Within that row, iridium sits in Group 9 (Transition Metals), alongside elements that share a similar number of valence electrons and, by extension, similar chemical behavior.
This position is not arbitrary — the periodic table was deliberately organized so that an element's row and column reveal its expected reactivity, bonding pattern, and physical state at a glance.
Physical & Chemical Properties
Iridium has an atomic mass of 192.217 u and a density of 22.56 g/cm³. Its melting point is 2446°C and its boiling point is 4428°C.
Iridium is malleable and ductile in its pure metallic form, and like other transition metals it can typically form more than one stable oxidation state.
Electron Configuration Explained
Iridium's electron configuration is [Xe] 4f¹⁴ 5d⁷ 6s², describing how its electrons are distributed across shells and subshells around the nucleus.
Reading the configuration in order shows electrons filling shells of increasing energy, following the standard Aufbau principle that explains how atomic structure builds up across the periodic table.
The outermost (valence) electrons shown in this configuration are what ultimately determine iridium's chemical reactivity and the type of bonds it forms with other elements.
History & Discovery
Iridium was formally discovered in 1803, Tennant, identified through the careful isolation and analytical techniques typical of that era's chemical research.
Many elements from this period were anticipated by Dmitri Mendeleev's periodic table, which successfully predicted gaps corresponding to undiscovered elements well before laboratory instruments existed to confirm them directly.
What Is Iridium Used For?
Iridium's specific properties make it useful in several applications, including:
- Crucibles
- Spark plugs
- Compass bearings
- Kilogram standard
- Pen tips
These uses reflect iridium's underlying classification as a transition metal, since the same properties that define its category in chemistry also determine where it becomes practically useful.
Fun Facts About Iridium
- An iridium-rich layer in rock sediment worldwide proved an asteroid killed the dinosaurs 66M years ago.
- Iridium is element number 77 on the periodic table, in Period 6 and Group 9.
- Its standard atomic mass is 192.217 u, calculated from the natural abundance of its isotopes.
Frequently Asked Questions
What is Iridium's atomic number?
Iridium has atomic number 77.
What is Iridium's chemical symbol?
Iridium's symbol is Ir.
What group and period is Iridium in?
Iridium is in Period 6, Group 9 (Transition Metals).
What is Iridium's atomic mass?
Iridium's standard atomic mass is 192.217 u.