Global InformationIridium information
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| Iridium | |||||||||||||||||||||||||||||||||
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| Pronunciation | /ɪˈrɪdiəm/ | ||||||||||||||||||||||||||||||||
| Appearance | Silvery white | ||||||||||||||||||||||||||||||||
| Standard atomic weight Ar°(Ir) | |||||||||||||||||||||||||||||||||
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| Iridium in the periodic table | |||||||||||||||||||||||||||||||||
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| Atomic number (Z) | 77 | ||||||||||||||||||||||||||||||||
| Group | group 9 | ||||||||||||||||||||||||||||||||
| Period | period 6 | ||||||||||||||||||||||||||||||||
| Block | d-block | ||||||||||||||||||||||||||||||||
| Electron configuration | [Xe] 4f14 5d7 6s2 | ||||||||||||||||||||||||||||||||
| Electrons per shell | 2, 8, 18, 32, 15, 2 | ||||||||||||||||||||||||||||||||
| Physical properties | |||||||||||||||||||||||||||||||||
| Phase at STP | solid | ||||||||||||||||||||||||||||||||
| Melting point | 2719 K (2446 °C, 4435 °F) | ||||||||||||||||||||||||||||||||
| Boiling point | 4403 K (4130 °C, 7466 °F) | ||||||||||||||||||||||||||||||||
| Density (at 20° C) | 22.562 g/cm3 [3] | ||||||||||||||||||||||||||||||||
| when liquid (at m.p.) | 19 g/cm3 | ||||||||||||||||||||||||||||||||
| Heat of fusion | 41.12 kJ/mol | ||||||||||||||||||||||||||||||||
| Heat of vaporization | 564 kJ/mol | ||||||||||||||||||||||||||||||||
| Molar heat capacity | 25.10 J/(mol·K) | ||||||||||||||||||||||||||||||||
Vapor pressure
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| Atomic properties | |||||||||||||||||||||||||||||||||
| Oxidation states | −3, –2, −1, 0, +1, +2, +3, +4, +5, +6, +7, +8, +9[4] | ||||||||||||||||||||||||||||||||
| Electronegativity | Pauling scale: 2.20 | ||||||||||||||||||||||||||||||||
| Ionization energies |
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| Atomic radius | empirical: 136 pm | ||||||||||||||||||||||||||||||||
| Covalent radius | 141±6 pm | ||||||||||||||||||||||||||||||||
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| Other properties | |||||||||||||||||||||||||||||||||
| Natural occurrence | primordial | ||||||||||||||||||||||||||||||||
| Crystal structure | face-centered cubic (fcc) (cF4) | ||||||||||||||||||||||||||||||||
| Lattice constant |  | ||||||||||||||||||||||||||||||||
| Thermal expansion | 6.47×10−6/K (at 20 °C)[3] | ||||||||||||||||||||||||||||||||
| Thermal conductivity | 147 W/(m⋅K) | ||||||||||||||||||||||||||||||||
| Electrical resistivity | 47.1 nΩ⋅m (at 20 °C) | ||||||||||||||||||||||||||||||||
| Magnetic ordering | paramagnetic[5] | ||||||||||||||||||||||||||||||||
| Molar magnetic susceptibility | +25.6 × 10−6 cm3/mol (298 K)[6] | ||||||||||||||||||||||||||||||||
| Young's modulus | 528 GPa | ||||||||||||||||||||||||||||||||
| Shear modulus | 210 GPa | ||||||||||||||||||||||||||||||||
| Bulk modulus | 320 GPa | ||||||||||||||||||||||||||||||||
| Speed of sound thin rod | 4825 m/s (at 20 °C) | ||||||||||||||||||||||||||||||||
| Poisson ratio | 0.26 | ||||||||||||||||||||||||||||||||
| Mohs hardness | 6.5 | ||||||||||||||||||||||||||||||||
| Vickers hardness | 1760–2200 MPa | ||||||||||||||||||||||||||||||||
| Brinell hardness | 1670 MPa | ||||||||||||||||||||||||||||||||
| CAS Number | 7439-88-5 | ||||||||||||||||||||||||||||||||
| History | |||||||||||||||||||||||||||||||||
| Discovery and first isolation | Smithson Tennant (1803) | ||||||||||||||||||||||||||||||||
| Isotopes of iridium | |||||||||||||||||||||||||||||||||
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Iridium is a chemical element; it has symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal (after osmium) with a density of 22.56 g/cm3 (0.815 lb/cu in)[8] as defined by experimental X-ray crystallography.[a] 191Ir and 193Ir are the only two naturally occurring isotopes of iridium, as well as the only stable isotopes; the latter is the more abundant. It is one of the most corrosion-resistant metals,[11] even at temperatures as high as 2,000 °C (3,630 °F).
Iridium was discovered in 1803 among insoluble impurities in natural platinum. Smithson Tennant, the primary discoverer, named it after the Greek goddess Iris, personification of the rainbow, because of the striking and diverse colors of its salts. Iridium is one of the rarest elements in Earth's crust, with estimated annual production and consumption of only 7.3 tonnes (16 thousand pounds) in 2018.[12]
The dominant uses of iridium are the metal itself and its alloys, as in high-performance spark plugs, crucibles for recrystallization of semiconductors at high temperatures, and electrodes for the production of chlorine in the chloralkali process. Important compounds of iridium are chlorides and iodides in industrial catalysis. Iridium is a component of some OLEDs.
Iridium is found in meteorites in much higher abundance than in the Earth's crust.[13] For this reason, the unusually high abundance of iridium in the clay layer at the Cretaceous–Paleogene boundary gave rise to the Alvarez hypothesis that the impact of a massive extraterrestrial object caused the extinction of dinosaurs and many other species 66 million years ago, now known to be produced by the impact that formed the Chicxulub crater. Similarly, an iridium anomaly in core samples from the Pacific Ocean suggested the Eltanin impact of about 2.5 million years ago.[14]
It is thought that the total amount of iridium in the planet is much higher than that observed in crustal rocks, but as with other platinum-group metals, the high density and tendency of iridium to bond with iron caused most iridium to descend below the crust when the planet was young and still molten.
- ^ "Standard Atomic Weights: Iridium". CIAAW. 2017.
- ^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
- ^ a b c Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.
- ^ Wang, Guanjun; Zhou, Mingfei; Goettel, James T.; Schrobilgen, Gary G.; Su, Jing; Li, Jun; Schlöder, Tobias; Riedel, Sebastian (2014). "Identification of an iridium-containing compound with a formal oxidation state of IX". Nature. 514 (7523): 475–477. Bibcode:2014Natur.514..475W. doi:10.1038/nature13795. PMID 25341786. S2CID 4463905.
- ^ Lide, D. R., ed. (2005). "Magnetic susceptibility of the elements and inorganic compounds". CRC Handbook of Chemistry and Physics (PDF) (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.
- ^ Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
- ^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
- ^ "Iridium – Element information, properties and uses | Periodic Table". www.rsc.org. Retrieved 2023-10-26.
- ^ Helmenstine, Anne Marie (May 6, 2022). "What is the Densest Element on the Periodic Table?". Thoughtco.com. Retrieved October 9, 2022.
- ^ Arblaster, J. W. (1989). "Densities of Osmium and Iridium Recalculations Based upon a Review of the Latest Crystallographic Data". Platinum Metals Rev. 33 (1): 14–16. doi:10.1595/003214089X3311416. S2CID 267570193.
- ^ "Iridium (Ir) | AMERICAN ELEMENTS". American Elements: The Materials Science Company. Retrieved 2023-11-22.
- ^ Singerling, Sheryl A.; Schulte, Ruth F. (August 2021). "Platinum-Group Metals". 2018 Minerals Yearbook (PDF). USGS. p. 57.11.
- ^ Becker, Luann (2002). "Repeated Blows" (PDF). Scientific American. 286 (3): 77–83. Bibcode:2002SciAm.286c..76B. doi:10.1038/scientificamerican0302-76. PMID 11857903. Retrieved January 19, 2016.
- ^ Kyte, Frank T.; Zhiming Zhou; John T. Wasson (1981). "High noble metal concentrations in a late Pliocene sediment". Nature. 292 (5822): 417–420. Bibcode:1981Natur.292..417K. doi:10.1038/292417a0. ISSN 0028-0836. S2CID 4362591.
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