Iridium

77

Ir

192.217(3)
  • Name: Iridium
  • Symbol: Ir
  • Atomic number: 77
  • Atomic weight: 192.217(3)
  • CAS Registry ID: 7439-88-5
  • Group name: Precious metal
  • Period number: 6
  • Block: d-block
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Description

Iridium is a transition metal that is a bright silver white color in its natural solid state. It can be attached by molten salts, but it has the strongest anti-corrosive properties of all the metal elements. Iridium has an atomic weight of 192.217, a melting point of 4471 °F, and a boiling point of 8002 °F. Some common uses of iridium include: as a component in platinum alloys as a hardening agent, as a component in crucibles that must withstand high temperatures, as a component in spark plugs, and in radiation therapy.

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Isolation

Iridium occurs in nature in alluvial deposits with other platinum group metals. It may also be obtained as a by-product of nickel processing.

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The isolation of iridium from its natural sources is extremely complicated and complex; the difficulties of iridium isolation make small scale laboratory isolation procedures for this element nearly impossible. The beginning isolation process involves treating the mineral containing iridium to remove any silver, gold, platinum, or palladium that are also present in the mineral. This step is carried out by treating the mineral with sodium bisulphate and melting the products. Next, the solution is extracted with water; this solution contains an insoluble residue of iridium. The residue is melted using sodium peroxide and then extracted again into water to remove any ruthenium and osmium salts that remain. Iridium oxide is left and it is dissolved using a mixture of hydrochloric acid and nitric acid. The result of this step yields a compound of iridium that contains chlorine and ammonium. Evaporation and drying under hydrogen gas burns off the remaining contaminants and results in pure iridium.
General
Name Iridium
Symbol Ir
Number 77
Chemical series transition metals
Group 9
Period 6
Block d
Appearance silvery white
Standard atomic weight 192.217(3)  g·mol−1
Electron configuration [Xe] 4f14 5d7 6s2
Electrons per shell 2, 8, 18, 32, 15, 2
Atomic properties
Crystal structure cubic face centered
Oxidation states 2, 3, 4, 6 (mildly basic oxide)
Electronegativity 2.20 (scale Pauling)
Ionization energies 1st: 880 kJ/mol
(more) 2nd: 1600 kJ/mol
(more)
Atomic radius 135 pm
Atomic radius (calc.) 180 pm
Covalent radius 137 pm
Van der Waals radius
Physical properties
Phase solid
Density (near r.t.) 22.42  g·cm−3
Liquid density at m.p. 19  g·cm−3
Melting point 2719 K (2446 °C, 4435 °F)
Boiling point 4701 K (4428 °C, 8002 °F)
Critical point
Heat of fusion 41.12  kJ·mol−1
Heat of vaporization 563  kJ·mol−1
Heat capacity (25 °C) 25.10  J·mol−1·K−1
Miscellaneous
Magnetic ordering
Electrical resistivity (20 °C) 47.1 n Ω·m
Thermal conductivity (300 K) 147  W·m−1·K−1
Thermal expansion (25 °C) 6.4  µm·m−1·K−1
Speed of sound (thin rod) (20 °C) 4825 m/s
Young's modulus 528 GPa
Shear modulus 210 GPa
Bulk modulus 320 GPa
Poisson ratio 0.26
Mohs hardness 6.5
Vickers hardness 1760 MPa
Brinell hardness 1670 MPa
CAS registry number 7439-88-5

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