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Periodic Table
Periodic

Iridium

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Iridium

Atomic Mass	192.217
Electron Configuration	[Xe]6s24f145d7
Oxidation States	+4, +3
Year Discovered	1803

Iridium

Atomic Mass	192.217
Electron Configuration	[Xe]6s24f145d7
Oxidation States	+4, +3
Year Discovered	1803

Identifiers

Element Name	Iridium
Element Symbol	Ir
InChI	InChI=1S/Ir
InChIKey	GKOZUEZYRPOHIO-UHFFFAOYSA-N

Properties

Atomic Weight	192.217(2) 192.217 192.2 192.217(3)
Electron Configuration	[Xe]6s²4f¹⁴5d⁷
Atomic Radius	Van der Waals Atomic Radius : 202 pm (Van der Waals) Empirical Atomic Radius : 135pm (Empirical) Covalent Atomic Radius : 141(6) pm (Covalent)
Oxidation States	+4, +3 -3, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
Ground Level	⁴F_9/2
Ionization Energy	9.1 eV 8.96702 ± 0.00022 eV
Electronegativity	Pauling Scale Electronegativity : 2.2(Pauling Scale) Allen Scale Electronegativity : 1.68(Allen Scale)
Electron Affinity	1.565eV 1.97eV
Atomic Spectra	Lines Holdings Levels Holdings
Physical Description	Solid
Element Classification	Metal
Element Period Number	6
Element Group Number	9
Density	22.42 grams per cubic centimeter
Melting Point	2719 K (2446°C or 4435°F) 2446°C
Boiling Point	4701 K (4428°C or 8002°F) 4130°C
Estimated Crustal Abundance	1×10^-3 milligrams per kilogram
Estimated Oceanic Abundance	Not Applicable

History

The name derives from the Latin Iris, the Greek goddess of rainbows, because of the variety of colours in the element's salt solutions. Iridium and osmium were both discovered in a crude platinum ore in 1803 by the English chemist Smithson Tennant. Iridium was discovered independently by the French chemist H. V. Collet-Descotils, who actually published his paper one month before Tennant, but Tennant is given credit for the discovery, perhaps because he alone also found osmium in the ore.

Iridium and osmium were discovered at the same time by the British chemist Smithson Tennant in 1803. Iridium and osmium were identified in the black residue remaining after dissolving platinum ore with aqua regia, a mixture of 25% nitric acid (HNO3) and 75% hydrochloric acid (HCl). Today, iridium is still obtained from platinum ores and as a by-product of mining nickel.

From the Latin word iris meaning rainbow. Tennant discovered iridium in 1803 in the residue left when crude platinum is dissolved by aqua regia. The name iridium is appropriate because its salts are highly colored.

Historical Atomic Weights

Year	Atomic Weight (uncertainty) [u]	Reference
2017	192.217(2)	https://doi.org/10.1515/pac-2019-0603
1993	192.217(3)	https://doi.org/10.1351/pac199466122423
1969	192.22(3)	https://doi.org/10.1351/pac197021010091
1953	192.2	https://doi.org/10.1039/JR9540004713
1909	193.1	https://doi.org/10.1021/ja01931a001
1902	193.0	https://doi.org/10.1007/BF01370337

Historical Isotopic Abundances

Year	Isotope	Abundance (uncertainty)	Reference
2017	¹⁹¹Ir	0.3723(9)
2017	¹⁹³Ir	0.6277(9)
1997	¹⁹¹Ir	0.373(2)	https://doi.org/10.1351/pac199870010217
1997	¹⁹³Ir	0.627(2)	https://doi.org/10.1351/pac199870010217
1979	¹⁹¹Ir	0.373(3)	https://doi.org/10.1351/pac198052102349
1979	¹⁹³Ir	0.627(3)	https://doi.org/10.1351/pac198052102349
1975	¹⁹¹Ir	0.373	https://doi.org/10.1351/pac197647010075
1975	¹⁹³Ir	0.627	https://doi.org/10.1351/pac197647010075

Description

Iridium, a metal of the platinum family, is white (similar to platinum) but with a slight yellowish cast. Because iridium is very hard and brittle, it is hard to machine, form, or work.

It is the most corrosion-resistant metal known, and was used in making the standard meter bar of Paris, which is a 90 percent platinum and 10 percent iridium alloy. This meter bar was replaced in 1960 as a fundamental unit of length (see Krypton).

Iridium is not attacked by any of the acids nor by aqua regia, but is attacked by molten salts, such as NaCl and NaCN. The specific gravity of iridium is to osmium's specific gravity. Calculations of the densities of iridium and osmium from the space lattices give values of 22.65 and 22.61 g/cm^3, respectively. These values may be more reliable than actual physical measurements for determining which element is heavier.

Users

Pure iridium is very brittle and is nearly impossible to machine. It is primarily used as a hardening agent for platinum. Platinum-iridium alloys are used to make crucibles and other high temperature equipment. Iridium is also alloyed with osmium to make the tips of fountain pens and compass bearings.

Iridium is the most corrosive resistant metal known. For this reason, the standard meter bar was created from an alloy of 90% platinum and 10% iridium. This bar was replaced as the definition of the meter in 1960 when the meter was redefined in terms of the orange-red spectral line of krypton-86.

A thin, worldwide layer of iridium exists in a layer of sediment that was put down at the end of the Cretaceous period. Since meteors and asteroids contain a higher percentage of iridium than the earth's crust, this iridium enriched layer is seen as evidence that the earth was struck by a large meteor or asteroid at that time. Dust from the impact would have spread around the globe, depositing the iridium. The dust also would have blocked the sun for a time, resulting in the extinction of many plant and animal species, including the dinosaurs.

Although its principal use is as a hardening agent for platinum, iridium is also used to make crucibles and devices requiring high temperatures. It is also used for electrical contacts.

The element forms an alloy with osmium which is used for tipping pens and compass bearings.

Sources

Iridium occurs uncombined in nature with platinum and other metals of this family in alluvial deposits. It is recovered as a by-product from the nickel mining industry.

Compounds

See more information at the Iridium compound page.

Element Forms

CID	Name	Formula	SMILES	Molecular Weight
23924	iridium	Ir	[Ir]	192.22
66373	iridium-192	Ir	[192Ir]	191.96260
168053	iridium(3+)	Ir+3	[Ir+3]	192.22
178173	iridium-194	Ir	[194Ir]	193.96508
185619	iridium-184	Ir	[184Ir]	183.9575
16097723	iridium-191	Ir	[191Ir]	190.96059
167365	iridium-188	Ir	[188Ir]	187.9588
177484	iridium-187	Ir	[187Ir]	186.9575
177690	iridium-195	Ir	[195Ir]	194.96598
178177	iridium-189	Ir	[189Ir]	188.9587
185569	iridium-186	Ir	[186Ir]	185.9579
185674	iridium-182	Ir	[182Ir]	181.9581
44146835	iridium-193	Ir	[193Ir]	192.96292
167220	iridium-190	Ir	[190Ir]	189.96054
185673	iridium-185	Ir	[185Ir]	184.9567

Isotopes

Stable Isotope Count	2

Isotopes in Industry

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].

Fig. IUPAC.77.1: This is a radiograph of a weld using ¹⁹²Ir as the source of radiation. The gamma rays given off by the isotope enable imperfections in the weld to be seen on the radiograph. (Photo Source: Hayward and Currie, 2006) [274].

[274] P. Hayward, D. Currie. “Radiography of welds using seleniuim 75, Ir 192 and x-rays”, in Asia-Pacific Conference on NDT, Auckland, New Zealand (2006).

Isotopes in Medicine

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.

[188] S. J. Adelstein, F. J. Manning. Isotopes for Medicine and the Life Sciences, pp. 20–25, National Academy Press, Washington DC (1995).

[521] A. Talamo, Y. Gohar. Radioactive Isotope Production for Medical Applications Using Kharkov Electron Driven Subcritical Assembly Facility, ANL-07/18, Argonne National Laboratory Argonne, Illinois (2007).

[522] S. A. Buzdar, M. A. Gadhi, M. A. Rao, N. A. Laghari, M. Anees. J. Pak. Med. Assoc.59, 113 (2009).

[523] T. Genkaa, S. Iwamotoa, E. Juitab, N. Takeuchia. Nucl. Inst. Methods Phys. Res. Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.369, 709 (1996).

[524] K. J. Kairemo, M. S. Kestilä, S. Savolainen, O. A. Korhola, J. V. Hiltunen, R. I. Svahn, E. T. Korppi Tommola, F. F. Knapp, C. Brihaye. J. Nucl. Biol. Med.38, 86 (1994).

[525] S. T. Treves, A. B. Packard, L. C. T. Fung. J. Nucl. Med.45, 508 (2004).

Isotopes Used as a Source of Radioactive Isotope(s)

Iridium consists of two stable isotopes (191Ir and 193Ir) from which the radioactive isotopes 192Ir and 195mPt (with a half-life of 4 days) can be produced. Both are used in nuclear medicine. The m in the superscript 195mPt indicates a metastable state of the isotope.

Isotope Mass and Abundance

Isotope	Atomic Mass (uncertainty) [u]	Abundance (uncertainty)
^191Ir	190.960 591(9)	0.3723(9)
^193Ir	192.962 924(9)	0.6277(9)

Isotope	Atomic Mass (uncertainty) [u]	Abundance (uncertainty)
¹⁹¹Ir	190.9605893(21)	0.373(2)
¹⁹³Ir	192.9629216(21)	0.627(2)

Atomic Mass, Half Life, and Decay

Nuclide	Atomic Mass and Uncertainty [u]	Half Life and Uncertainty	Discovery Year	Decay Modes, Intensities and Uncertainties [%]
¹⁶³Ir	162.994299 ± 0.000429 [Estimated]	Not-specified		p ?
¹⁶⁴Ir	163.991966 ± 0.000339 [Estimated]	1 ms [Estimated]		p ?; α ?; β⁺ ?
¹⁶⁴Ir^m	163.991966 ± 0.000339 [Estimated]	70 us ± 10	2001	p=?; α=4±0.2%; β⁺ ?
¹⁶⁵Ir	164.987552 ± 0.00017 [Estimated]	50 ns [Estimated]		p ?; α ?
¹⁶⁵Ir^m	164.987552 ± 0.00017 [Estimated]	325 us ± 33	1997	p=88±0.2%; α=12±0.2%
¹⁶⁶Ir	165.985716 ± 0.000215 [Estimated]	10.5 ms ± 2.2	1981	α=93±0.3%; p=7±0.3%
¹⁶⁶Ir^m	165.985716 ± 0.000215 [Estimated]	15.1 ms ± 0.9	1996	α=98.2±0.6%; p=1.8±0.6%
¹⁶⁷Ir	166.981671973 ± 0.000019694	29.3 ms ± 0.6	1981	α=43.5±1.9%; p=38.6±1.2%; β⁺ ?
¹⁶⁷Ir^m	166.981671973 ± 0.000019694	28.5 ms ± 0.5	1995	α=89±0.3%; β⁺ ?; p=0.41±0.6%
¹⁶⁸Ir	167.979960978 ± 0.000059277	230 ms ± 50	1978	α≈100%; β⁺ ?; β⁺p ?
¹⁶⁸Ir^m	167.979960978 ± 0.000059277	163 ms ± 16	1996	α=77±0.9%; β⁺ ?; β⁺p ?
¹⁶⁹Ir	168.976281743 ± 0.00002502	353 ms ± 4	1978	α=53±0.7%; β⁺ ?
¹⁶⁹Ir^m	168.976281743 ± 0.00002502	280 ms ± 1	1984	α=79±0.5%; β⁺ ?; p ?
¹⁷⁰Ir	169.975113 ± 0.000109 [Estimated]	910 ms ± 150	1977	β⁺ ?; α=5.2±1.7%
¹⁷⁰Ir^m	169.975113 ± 0.000109 [Estimated]	811 ms ± 18	1977	α=38±0.5%; β⁺ ?; IT ?
¹⁷¹Ir	170.971645520 ± 0.000041295	3.1 s ± 0.3	1967	β⁺ ?; α=15±0.2%
¹⁷¹Ir^m	170.971645520 ± 0.000041295	1.47 s ± 0.06	1967	α=54±0.5%; β⁺ ?; p ?
¹⁷²Ir	171.970607035 ± 0.000034785	4.4 s ± 0.3	1967	β⁺≈98%; α≈2%
¹⁷²Ir^m	171.970607035 ± 0.000034785	2.19 s ± 0.07	1967	β⁺=90.5±1.1%; α=9.5±1.1%
¹⁷³Ir	172.967505477 ± 0.000011316	9.0 s ± 0.8	1967	β⁺=96.5±2%; α=3.5±2%
¹⁷³Ir^m	172.967505477 ± 0.000011316	2.20 s ± 0.05	1967	β⁺=88±0.1%; α=12±0.1%
¹⁷⁴Ir	173.966949939 ± 0.000012046	7.9 s ± 0.6	1967	β⁺=99.5±0.3%; α=0.5±0.3%
¹⁷⁴Ir^m	173.966949939 ± 0.000012046	4.9 s ± 0.3	1992	β⁺=97.5±0.3%; α=2.5±0.3%
¹⁷⁵Ir	174.964149519 ± 0.000013295	9 s ± 2	1967	β⁺=99.15±2.8%; α=0.85±2.8%
¹⁷⁵Ir^m	174.964149519 ± 0.000013295	33 s ± 4	1967	β⁺= ?; IT ?
¹⁷⁵Irⁿ	174.964149519 ± 0.000013295	6.58 us ± 0.15	2019	IT=100%
¹⁷⁶Ir	175.963626261 ± 0.000008679	8.7 s ± 0.5	1967	β⁺=96.9±0.6%; α=3.1±0.6%
¹⁷⁶Ir^m	175.963626261 ± 0.000008679	10 s [Estimated]		β⁺= ?; IT ?
¹⁷⁷Ir	176.961301500 ± 0.000021213	29.8 s ± 1.7	1967	β⁺≈100%; α=0.06±0.1%
¹⁷⁷Ir^m	176.961301500 ± 0.000021213	>100 ns		IT=100%
¹⁷⁷Irⁿ	176.961301500 ± 0.000021213	>100 ns	1991	IT=100%
¹⁷⁸Ir	177.961079395 ± 0.000020204	12 s ± 2	1972	β⁺=100%
¹⁷⁹Ir	178.959117594 ± 0.000010489	79 s ± 1	1992	β⁺=100%
¹⁸⁰Ir	179.959229446 ± 0.000023302	1.5 m ± 0.1	1972	β⁺=100%
¹⁸¹Ir	180.957634691 ± 0.000005631	4.90 m ± 0.15	1972	β⁺=100%
¹⁸¹Ir^m	180.957634691 ± 0.000005631	298 ns	1992	IT=100%
¹⁸¹Irⁿ	180.957634691 ± 0.000005631	126 ns ± 6	1992	IT=100%
¹⁸²Ir	181.958076296 ± 0.000022509	15.0 m ± 1.0	1961	β⁺=100%
¹⁸²Ir^m	181.958076296 ± 0.000022509	170 ns ± 40	1990	IT=100%
¹⁸²Irⁿ	181.958076296 ± 0.000022509	130 ns ± 50	1990	IT=100%
¹⁸³Ir	182.956841231 ± 0.000026486	58 m ± 5	1961	β⁺≈100%; α ?
¹⁸⁴Ir	183.957476000 ± 0.00003	3.09 h ± 0.03	1960	β⁺=100%
¹⁸⁴Ir^m	183.957476000 ± 0.00003	470 us ± 30	1988	IT=100%
¹⁸⁴Irⁿ	183.957476000 ± 0.00003	350 ns ± 90	1988	IT=100%
¹⁸⁵Ir	184.956698000 ± 0.00003	14.4 h ± 0.1	1958	β⁺=100%
¹⁸⁵Ir^m	184.956698000 ± 0.00003	120 ns ± 20	1979	IT=100%
¹⁸⁶Ir	185.957946754 ± 0.00001774	16.64 h ± 0.03	1958	β⁺=100%
¹⁸⁶Ir^m	185.957946754 ± 0.00001774	1.92 h ± 0.05	1962	β⁺≈75%; IT≈25%
¹⁸⁷Ir	186.957542000 ± 0.00003	10.5 h ± 0.3	1958	β⁺=100%
¹⁸⁷Ir^m	186.957542000 ± 0.00003	30.3 ms ± 0.6	1963	IT=100%
¹⁸⁷Irⁿ	186.957542000 ± 0.00003	152 ns ± 12	1969	IT=100%
¹⁸⁷Ir^p	186.957542000 ± 0.00003	1.8 us ± 0.5	2010	IT=100%
¹⁸⁸Ir	187.958834999 ± 0.000010116	41.5 h ± 0.5	1950	β⁺=100%
¹⁸⁸Ir^m	187.958834999 ± 0.000010116	4.15 ms ± 0.15	1971	IT≈100%; β⁺ ?
¹⁸⁹Ir	188.958722602 ± 0.0000135	13.2 d ± 0.1	1955	ε=100%
¹⁸⁹Ir^m	188.958722602 ± 0.0000135	13.3 ms ± 0.3	1960	IT=100%
¹⁸⁹Irⁿ	188.958722602 ± 0.0000135	3.7 ms ± 0.2	1975	IT=100%
¹⁹⁰Ir	189.960543374 ± 0.00000147	11.78 d ± 0.10	1947	β⁺=100%; e⁺<0.002%
¹⁹⁰Ir^m	189.960543374 ± 0.00000147	1.120 h ± 0.003	1964	IT=100%
¹⁹⁰Irⁿ	189.960543374 ± 0.00000147	>2 us	1996	IT=100%
¹⁹⁰Ir^p	189.960543374 ± 0.00000147	3.087 h ± 0.012	1950	β⁺=91.4±0.2%; IT=8.6±0.2%
¹⁹¹Ir	190.960591455 ± 0.000001406	Stable	1935	IS=37.3±0.2%
¹⁹¹Ir^m	190.960591455 ± 0.000001406	4.899 s ± 0.023	1955	IT=100%
¹⁹¹Irⁿ	190.960591455 ± 0.000001406	5.7 s ± 0.4	1979	IT=100%
¹⁹²Ir	191.962602414 ± 0.00000141	73.820 d ± 0.014	1937	β^-=95.24±0.4%; ε=4.76±0.4%
¹⁹²Ir^m	191.962602414 ± 0.00000141	1.45 m ± 0.05	1937	IT≈100%; β^-=0.0175%
¹⁹²Irⁿ	191.962602414 ± 0.00000141	241 y ± 9	1959	IT=100%
¹⁹³Ir	192.962923753 ± 0.000001425	Stable	1935	IS=62.7±0.2%
¹⁹³Ir^m	192.962923753 ± 0.000001425	10.53 d ± 0.04	1957	IT=100%
¹⁹³Irⁿ	192.962923753 ± 0.000001425	124.8 us ± 2.1	2012	IT=100%
¹⁹⁴Ir	193.965075703 ± 0.000001429	19.35 h ± 0.07	1937	β^-=100%
¹⁹⁴Ir^m	193.965075703 ± 0.000001429	31.85 ms ± 0.24	1959	IT=100%
¹⁹⁴Irⁿ	193.965075703 ± 0.000001429	171 d ± 11	1968	β^-=100%
¹⁹⁵Ir	194.965976898 ± 0.000001431	2.29 h ± 0.17	1952	β^-=100%
¹⁹⁵Ir^m	194.965976898 ± 0.000001431	3.74 h ± 0.07	1968	β^-≈100%; IT ?
¹⁹⁵Irⁿ	194.965976898 ± 0.000001431	4.4 us ± 0.6	2011	IT=100%
¹⁹⁶Ir	195.968399669 ± 0.000041239	52.0 s ± 1.1	1966	β^-=100%
¹⁹⁶Ir^m	195.968399669 ± 0.000041239	1.40 h ± 0.02	1959	β^-≈100%; IT ?
¹⁹⁷Ir	196.969657217 ± 0.000021588	5.8 m ± 0.5	1952	β^-=100%
¹⁹⁷Ir^m	196.969657217 ± 0.000021588	8.9 m ± 0.3	1976	β^-≈100%; IT ?
¹⁹⁷Irⁿ	196.969657217 ± 0.000021588	30 us ± 8	2005	IT=100%
¹⁹⁷Ir^p	196.969657217 ± 0.000021588	15 us ± 9	2005	IT=100%
¹⁹⁸Ir	197.972399 ± 0.000215 [Estimated]	8.7 s ± 0.4	1973	β^-=100%
¹⁹⁹Ir	198.973807097 ± 0.000044073	7 s ± 5	1993	β^-=100%
²⁰⁰Ir	199.976844 ± 0.00021 [Estimated]	43 s ± 6	2008	β^-=100%; β^-n ?
²⁰¹Ir	200.978701 ± 0.000215 [Estimated]	21 s ± 5	2008	β^-=100%
²⁰²Ir	201.982136 ± 0.000322 [Estimated]	11 s ± 3	2008	β^-=100%
²⁰²Ir^m	201.982136 ± 0.000322 [Estimated]	3.4 us ± 0.6	2011	IT=100%
²⁰³Ir	202.984573 ± 0.000429 [Estimated]	7 s >300ns [Estimated]	2009	β^- ?
²⁰³Ir^m	202.984573 ± 0.000429 [Estimated]	>100 ns [Estimated]		IT ?; β^- ?
²⁰³Irⁿ	202.984573 ± 0.000429 [Estimated]	798 ns ± 350	2011	IT=100%
²⁰⁴Ir	203.989726 ± 0.000429 [Estimated]	2 s >300ns [Estimated]	2011	β^- ?; β^-n ?
²⁰⁵Ir	204.993988 ± 0.000537 [Estimated]	1 s >300ns [Estimated]	2012	β^- ?; β^-n ?

Information Sources

1. PubChem

https://pubchem.ncbi.nlm.nih.gov
2. Atomic Mass Data Center (AMDC), International Atomic Energy Agency (IAEA)

LICENSE
https://www-nds.iaea.org/disclaimer.html

Ir
https://www-nds.iaea.org/amdc/
3. IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW)

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http://www.ciaaw.org/bylaws.htm

Iridium
https://www.ciaaw.org/iridium.htm
4. Jefferson Lab, U.S. Department of Energy

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Please see citation and linking information https https://www.jlab.org/privacy-and-security-notice

Iridium
https://education.jlab.org/itselemental/ele077.html
5. Los Alamos National Laboratory, U.S. Department of Energy

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https://about.lanl.gov/lanl-resources/web-policies/

Iridium
https://periodic.lanl.gov/77.shtml
6. NIST Physical Measurement Laboratory

LICENSE
https://www.nist.gov/pml/database-disclaimer

Iridium
https://physics.nist.gov/cgi-bin/Elements/elInfo.pl?element=77
7. IUPAC Periodic Table of the Elements and Isotopes (IPTEI)

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Copyright (c) 2020 International Union of Pure and Applied Chemistry. The International Union of Pure and Applied Chemistry (IUPAC) contribution within Pubchem is provided under a CC-BY-NC-ND 4.0 license, unless otherwise stated.
https://creativecommons.org/licenses/by-nc-nd/4.0/

https://doi.org/10.1515/pac-2015-0703
8. PubChem Elements

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https://www.nlm.nih.gov/copyright.html

Iridium

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