IRIDIUM

Introduction

Atomic Number: 77
Group: 9 or VIII B
Atomic Weight: 192.217
Period: 6
CAS Number: 7439-88-5

Classification

Chalcogen
Halogen
Noble Gas
Lanthanoid
Actinoid
Rare Earth Element
Platinum Group Metal
Transuranium
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
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

Electron Configuration: [Xe] 6s2 4f14 5d7
Block: d
Highest Occupied Energy Level: 6
Valence Electrons: 

Quantum Numbers:

n = 5
ℓ = 2
m = -1
ms = -½

Bonding

Electronegativity (Pauling scale):5 2.2
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

Specific Heat: 0.131 J/g°C 9 = 25.180 J/mol°C = 0.031 cal/g°C = 6.018 cal/mol°C
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 -  Crust:  0.001 mg/kg = 0.0000001% 15
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

Safety Information


Material Safety Data Sheet - ACI Alloys, Inc.

For More Information

External Links:

Sources

(1) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:16.
(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.