Chemical element · reference page

77Ir

Iridium

Iridium is element 77 (Ir), located in period 6, group 9 and the d block. At room temperature its reference phase is solid. Its electron configuration is [Xe] 4f14 5d7 6s2.

Atomic number77

Standard atomic weight192.217(2)

Group9

Period6

Blockd

Electron configuration[Xe] 4f14 5d7 6s2

Electronic structure

What controls its chemistry

The d subshell participates in the chemistry of iridium. Transition metals can use electrons of similar energies in bonding, which is why variable oxidation states, coordination compounds and catalytic behaviour are common across the d block.

Its electron configuration, [Xe] 4f14 5d7 6s2, should be read together with the oxidation state of the compound: removing electrons changes which d orbitals are occupied and can alter colour, magnetism, bonding and reactivity.

Chemical forms

Compounds, ions and materials

For iridium, important chemical forms include metals and alloys, oxides, halides and coordination compounds. Variable oxidation states are common because s and d electrons have similar energies, and ligands around the metal ion can strongly alter colour, magnetism and reactivity.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The listed density is 22.56 g/cm³. The melting point is 2 719 K (2 446 °C). The boiling point is 4 403 K (4 130 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where iridium is found and used

In practice, iridium is encountered in spark plugs, crucibles and electronics.

In practice

Examples of real uses

Spark plugs

Iridium-containing heat- and corrosion-resistant alloys are used in electrodes that must survive repeated electrical discharge and combustion temperatures.

Crucibles

High-temperature and corrosion-resistant materials containing the element are used to hold reactive melts or laboratory samples.

Electronics

Iridium is used in electronic components or materials where conductivity, semiconducting behaviour, optical response or chemical stability is useful.

Periodic position

What its neighbours tell us

Iridium is in period 6 and group 9. In the neighbourhood shown here, it lies between osmium and platinum in the same period; rhodium is above it and meitnerium below it in the same group. These positions make it possible to compare atomic size, ionisation energy and bonding behaviour with nearby elements.

Reference data

Physical and atomic properties

Classificationtransition metal

Phase at room temperatureSolid

Electron shells2 · 8 · 18 · 32 · 15 · 2

Density22.56 g/cm³

Melting point2 719 K (2 446 °C)

Boiling point4 403 K (4 130 °C)

Pauling electronegativity2.2

First ionisation energy865kJ/mol

Electron affinity150.9 kJ/mol

Values describe the element or neutral atom where applicable. Physical data can depend on allotrope, pressure and measurement conditions.

History

Discovery and identification

The discovery of iridium is associated with Smithson Tennant. Recognition of the element, isolation of a pure sample and assignment of its modern atomic number did not necessarily occur at the same time.

Isotopes and atomic weight

How isotope composition changes the numbers

The standard atomic weight is 192.217(2). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

Iridium has at least one stable isotope. Different isotopes have the same number of protons and therefore the same element identity, but different neutron numbers and atomic masses.

Safety

Handling and exposure

The hazards associated with iridium depend on chemical form, dose and route of exposure. Pure iridium, its ions and its compounds can have very different biological and environmental effects, so safety data should be checked for the actual substance being handled.