Periodic Table

Iridium

Transition Metal

Quick Facts about Iridium

Os
  • solid- state of matter at room temperature
  • Stable- has at least one stable isotope
  • +4, +3- common oxidation states in compounds
  • FCC- crystal structure, atomic arrangement in solid form
Pt

Iridium (Ir) is element 77 on the periodic table. Atomic mass of Ir: 192.2200 u. Ir is in period 6, group 9. Melting point of Ir: 2719.00 K.Density of Ir: 22.56 g/cm³.

Why Iridium Matters

Iridium in everyday life and industry

In Your Home

  • Iridium spark plugs in high-performance vehicles offer longer life

Industry Uses

AerospaceSpark plug electrodes in aircraft and racing engines use iridium
MaterialsCrucibles for growing sapphire and other high-quality crystals use iridium
MetrologyThe international prototype kilogram (until 2019) was platinum-iridium alloy
Oil & GasDeep-sea drilling equipment uses iridium alloys for corrosion resistance

In Your Body

✗ Not essential

Iridium has no known biological role. Some iridium compounds are being researched for cancer treatment. Iridium is found in the K-Pg boundary layer linked to dinosaur extinction.

Safety: The metal is generally non-toxic due to its inertness. Iridium compounds should be considered toxic.

Discovery of Iridium

Discovered by S.Tenant, A.F.Fourcory, L.N.Vauquelin, H.V.Collet-Descoltils in England/France, 1804

Name origin: Latin: iris (rainbow).

History & Events

1803
Named from Greek goddess Iris (rainbow) for its colorful compounds
1803
Discovered by Smithson Tennant in 1803 alongside osmium
1803
Asteroid impact theory was supported by iridium layer in Earth's crust
1803
Second densest element after osmium

About Iridium

The most corrosion-resistant metal known, attacked by no acid at any temperature. Second densest element after osmium at 22.56 g/cm3. Named for Greek goddess Iris (rainbow) because its salts display many colors. The famous K-Pg boundary iridium anomaly—a thin layer worldwide enriched 30× in iridium—provided key evidence for the asteroid impact that ended the dinosaurs 66 million years ago.

Atomic Properties of Ir

Atomic Number of Ir
77
Atomic Mass of Ir
192.2200 u
Electron Configuration
[Xe] 4f14 5d7 6s2
Electronegativity
2.20
Block
d-block
Group
9
Period
6

Physical Properties of Ir

Phase (STP)
solid
Melting Point of Ir
2719.00 K
Boiling Point of Ir
4403.00 K
Density of Ir
22.5600 g/cm3

Thermal Properties

Heat of Fusion
27.61 kJ/mol
Heat of Vaporization
604.00 kJ/mol
Specific Heat
0.13 J/g·K
Molar Heat Capacity
25.10 J/mol·K
Thermal Conductivity
147.00 W/m·K

Atomic Radii

Calculated
135 pm
Covalent
122 pm
Van der Waals
213 pm
Metallic
127 pm

Common Misconceptions

Wrong:Iridium on Earth came from asteroids.
Correct:While asteroid impacts deposit iridium (like the K-Pg boundary layer), most terrestrial iridium originates from Earth's core and reaches the surface through volcanic and tectonic processes.
Wrong:The iridium layer proves the dinosaurs were killed by an asteroid.
Correct:The K-Pg iridium anomaly is strong evidence for an impact, but the extinction involved multiple factors including volcanism (Deccan Traps). The iridium layer supports but doesn't prove the asteroid was the sole cause.
Wrong:Iridium is the hardest metal.
Correct:Iridium is extremely hard but chromium, tungsten, and osmium are harder. Iridium's claim to fame is being the most corrosion-resistant metal known and second densest element.

Isotopes of Iridium

Iridium has 2 naturally occurring isotopes, plus 1 notable radioactive isotope.

IsotopeAtomic Mass (u)AbundanceHalf-LifeDecay Mode
19177Ir (Ir-191)Iridium-191 isotope190.960589337.30%
19277Ir (Ir-192)Iridium-192 isotope191.96260%73.8 daysβ⁻, EC, β⁺
19377Ir (Ir-193)Iridium-193 isotope192.962921662.70%

Data source: NIH PubChem (aggregated from IUPAC, NIST)

Isotope Applications

Isotopes of Iridium have important real-world applications in science and industry.

Industrial Applications

Metallic 192Ir (with a half-life of 74 days) is used as a radiation source in gamma cameras for non-destructive testing of products for manufacturing flaws, such as aircraft parts, boilers, and pipeline welds (Fig. IUPAC.77.1) [274].

Medical Applications

Metallic 192Ir is used in brachytherapy [188], [521], [522], [523]. 191mIr (with a half-life of 5 s) is used for blood flow imaging (angiography), especially in pediatric populations [524], [525]. The m in the superscript 191mIr indicates a metastable state of the isotope.

Abundance

Earth's Crust
1.00 μg/kg

Uses

Used with osmium to tip gold pen points, to make crucible and special containers. Also to make alloys used for standard weights and measures, and heat-resistant alloys. Also as hardening agent for platinum.

Sources

Found in gravel deposits with platinum.

Geochemistry

Goldschmidt
siderophile
Geochemical Class
noble metal

Test Your Knowledge

Loading quiz...