Introduction
Group: 9 or VIII B
Atomic Weight: 192.217
Period: 6
CAS Number: 7439-88-5
Classification
No Stable Isotopes
Solid
Liquid
Gas
Solid (Predicted)
Description • Uses/Function
Discovered in 1803 by Tennant in the residue left when crude platinum is dissolved by aqua regia. The name iridium is appropriate, for its salts are highly colored. Iridium,a metal of the platinum family, is white, similar to platinum, but with a slight yellowish cast. It is very hard and brittle, making it very 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% platinum-10%iridium alloy. This meter bar was replaced in 1960 as a fundamental unit of length (see under Krypton). Iridium is not attacked by any of the acidsnor by aqua regia, but is attacked by molten salts, such as NaCl and NaCN. Iridium occurs uncombined in nature with platinum and other metals ofthis family in alluvial deposits. It is recovered as a by-product from the nickel mining industry. The presence of iridium has recently been used inexamining the Cretaceous-Tertiary (K-T) boundary. Meteorites contain small amounts of iridium. Because iridium is found widely distributed at theK-T boundary, it has been suggested that a large meteorite or asteroid collided with the earth, killing the dinosaurs, and creating a large dust cloudand crater. Searches for such a crater point to one in the Yucatan, known as Chicxulub. Iridium has found use in making crucibles and apparatus foruse at high temperatures. It is also used for electrical contacts. Its principal use is as a hardening agent for platinum. With osmium, it forms an alloywhich is used for tipping pens and compass bearings. The specific gravity of iridium is only very slightly lower than that of osmium, which has beengenerally credited as being the heaviest known element. Calculations of the densities of iridium and osmium from the space lattices gives values of22.65 and 22.61 g/cm^3, respectively. These values may be more reliable than actual physical measurements. Natural iridium contains two isotopes.Forty two other isotopes, all radioactive, are now recognized. At present, therefore, we know that either iridium or osmium is the densest knownelement, but the data do not yet allow selection between the two. Iridium costs about $50/g. 1
• "In addition to hardening platinum, iridium is used to tip gold pens. A platinum-iridium alloy is used for standard weights and measures. Iridium black is an important catalyst." 2
Physical Properties
Melting Point:3* 2446 °C = 2719.15 K = 4434.8 °F
Electron Configuration: [Xe] 6s2 4f14 5d7
n = 5
Electronegativity (Pauling scale):5 2.2
Specific Heat: 0.131 J/g°C 9 = 25.180 J/mol°C = 0.031 cal/g°C = 6.018 cal/mol°C
Earth -
Crust:
0.001 mg/kg = 0.0000001% 15
External Links:
(1) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:16.
Boiling Point:3* 4428 °C = 4701.15 K = 8002.4 °F
Sublimation Point:3
Triple Point:3
Critical Point:3
Density:4 22.5 g/cm3
* - at 1 atm
Electron Configuration
Block: d
Highest Occupied Energy Level: 6
Valence Electrons:
Quantum Numbers:
ℓ = 2
mℓ = -1
ms = -½
Bonding
Electropositivity (Pauling scale): 1.8
Electron Affinity:6 1.5638 eV
Oxidation States: +4,3,6
Work Function:7 5.6 eV = 8.9712E-19 J
Ionization Potential
eV 8
kJ/mol
Ionization Potential
eV 8
kJ/mol
Ionization Potential
eV 8
kJ/mol
1
8.967
865.2
Thermochemistry
Thermal Conductivity: 147 (W/m)/K, 27°C 10
Heat of Fusion: 26.1 kJ/mol 11 = 135.8 J/g
Heat of Vaporization: 604 kJ/mol 12 = 3142.3 J/g
State of Matter
Enthalpy of Formation (ΔHf°)13
Entropy (S°)13
Gibbs Free Energy (ΔGf°)13
(kcal/mol)
(kJ/mol)
(cal/K)
(J/K)
(kcal/mol)
(kJ/mol)
(s)
0
0
8.48
35.48032
0
0
(g)
159.0
665.256
46.240
193.46816
4.968
20.786112
Isotopes
Nuclide
Mass 14
Half-Life 14
Nuclear Spin 14
Binding Energy
164Ir
163.99220(44)#
1# ms
2-#
1,272.77 MeV
165Ir
164.98752(23)#
<1# μs
1/2+#
1,290.15 MeV
166Ir
165.98582(22)#
10.5(22) ms
(2-)
1,298.23 MeV
167Ir
166.981665(20)
35.2(20) ms
1/2+
1,306.30 MeV
168Ir
167.97988(16)#
161(21) ms
high
1,323.68 MeV
169Ir
168.976295(28)
780(360) ms [0.64(+46-24) s]
1/2+#
1,331.75 MeV
170Ir
169.97497(11)#
910(150) ms [0.87(+18-12) s]
low#
1,339.83 MeV
171Ir
170.97163(4)
3.6(10) s [3.2(+13-7) s]
1/2+#
1,347.90 MeV
172Ir
171.97046(11)#
4.4(3) s
(3+)
1,355.97 MeV
173Ir
172.967502(15)
9.0(8) s
(3/2+,5/2+)
1,373.35 MeV
174Ir
173.966861(30)
7.9(6) s
(3+)
1,381.43 MeV
175Ir
174.964113(21)
9(2) s
(5/2-)
1,389.50 MeV
176Ir
175.963649(22)
8.3(6) s
1,397.57 MeV
177Ir
176.961302(21)
30(2) s
5/2-
1,405.64 MeV
178Ir
177.961082(21)
12(2) s
1,413.71 MeV
179Ir
178.959122(12)
79(1) s
(5/2)-
1,431.10 MeV
180Ir
179.959229(23)
1.5(1) min
(4,5)(+#)
1,439.17 MeV
181Ir
180.957625(28)
4.90(15) min
(5/2)-
1,447.24 MeV
182Ir
181.958076(23)
15(1) min
(3+)
1,455.31 MeV
183Ir
182.956846(27)
57(4) min
5/2-
1,463.38 MeV
184Ir
183.95748(3)
3.09(3) h
5-
1,471.45 MeV
185Ir
184.95670(3)
14.4(1) h
5/2-
1,479.53 MeV
186Ir
185.957946(18)
16.64(3) h
5+
1,487.60 MeV
187Ir
186.957363(7)
10.5(3) h
3/2+
1,495.67 MeV
188Ir
187.958853(8)
41.5(5) h
1-
1,503.74 MeV
189Ir
188.958719(14)
13.2(1) d
3/2+
1,511.81 MeV
190Ir
189.9605460(18)
11.78(10) d
4-
1,510.57 MeV
191Ir
190.9605940(18)
STABLE
3/2+
1,518.64 MeV
192Ir
191.9626050(18)
73.827(13) d
4+
1,526.71 MeV
193Ir
192.9629264(18)
STABLE
3/2+
1,534.78 MeV
194Ir
193.9650784(18)
19.28(13) h
1-
1,542.85 MeV
195Ir
194.9659796(18)
2.5(2) h
3/2+
1,550.92 MeV
196Ir
195.96840(4)
52(1) s
(0-)
1,559.00 MeV
197Ir
196.969653(22)
5.8(5) min
3/2+
1,567.07 MeV
198Ir
197.97228(21)#
8(1) s
1,565.82 MeV
199Ir
198.97380(4)
20# s
3/2+#
1,573.89 MeV
Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses. 14
Abundance
Earth -
Total:
840 ppb 16
Mercury -
Total:
650 ppb 16
Venus -
Total:
890 ppb 16
Chondrites - Total: 0.35 (relative to 106 atoms of Si) 17
Compounds
iridium(II) chloride
iridium(II) iodide
iridium(II) oxide dihydrate
iridium(III) bromide
iridium(III) chloride; iridium trichloride
iridium(III) fluoride
Safety Information
Material Safety Data Sheet - ACI Alloys, Inc.
For More Information
American Elements
Chemical & Engineering News
Chemical Elements
ChemGlobe
Chemicool
Environmental Chemistry
Sources
(2) - Brownlee, Raymond B., Fuller, Robert W., and Whitsit, Jesse E. Elements of Chemistry; Allyn and Bacon: Boston, Massachusetts, 1959; p 545.
(3) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:132.
(4) - Lide, David R. CRC Handbook of Chemistry and Physics, 84th ed.; CRC Press: Boca Raton, FL, 2002; p 4:39-4:96.
(5) - Dean, John A. Lange's Handbook of Chemistry, 11th ed.; McGraw-Hill Book Company: New York, NY, 1973; p 4:8-4:149.
(6) - Lide, David R. CRC Handbook of Chemistry and Physics, 84th ed.; CRC Press: Boca Raton, FL, 2002; p 10:147-10:148.
(7) - Speight, James. Lange's Handbook of Chemistry, 16th ed.; McGraw-Hill Professional: Boston, MA, 2004; p 1:132.
(8) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 10:178 - 10:180.
(9) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:133.
(10) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:193, 12:219-220.
(11) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:123-6:137.
(12) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:107-6:122.
(13) - Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:4-9:94.
(14) - Atomic Mass Data Center. http://amdc.in2p3.fr/web/nubase_en.html (accessed July 14, 2009).
(15) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 14:17.
(16) - Morgan, John W. and Anders, Edward, Proc. Natl. Acad. Sci. USA 77, 6973-6977 (1980)
(17) - Brownlow, Arthur. Geochemistry; Prentice-Hall, Inc.: Englewood Cliffs, NJ, 1979, pp 15-16.