CURIUM

Introduction

Atomic Number: 96
Group: None
Atomic Weight: 247
Period: 7
CAS Number: 7440-51-9

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

Although curium follows americium in the periodic system, it was actually known before americium and was the third transuranium element to be discovered. It was identified by Seaborg, James, and Ghiorso in 1944 at the wartime Metallurgical Laboratory in Chicago as a result of helium-ion bombardment of 239Pu in the Berkeley, California, 60-inch cyclotron. Visible amounts (30 micrograms) of 242Cm, in the form of the hydroxide, were first isolated by Werner and Perlman of the University of California in 1947. In 1950, Crane, Wallmann, and Cunningham found that the magnetic susceptibility of microgram samples of Cmf3 was of the same magnitude as that of Gdf3. This provided direct experimental evidence for assigning an electronic configuration to Cm+3. In 1951, the same workers prepared curium in its elemental form for the first time. Sixteen isotopes of curium are now known. The most stable, 247Cm, with a half-life of 16 million years, is so short compared to the earth’s age that any primordial curium must have disappeared long ago from the natural scene. Minute amounts of curium probably exist in natural deposits of uranium, as a result of a sequence of neutron captures and beta decays sustained by the very low flux of neutrons naturally present in uranium ores. The presence of natural curium, however, has never been detected. 242Cm and 244Cm are available in multigram quantities. 248Cm has been produced only in milligram amounts. Curium is similar in some regards to gadolinium, its rareearth homolog, but it has a more complex crystal structure. Curium is silver in color, is chemically reactive, and is more electropositive than aluminum. CmO2, Cm2O3, Cmf3, Cmf4, CmCl3, CmBr3, and CmI3 have been prepared. Most compounds of trivalent curium are faintly yellow in color. 242Cm generates about three watts of thermal energy per gram. This compares to one-half watt per gram of 238Pu. This suggests use for curium as a power source. 244Cm is now offered for sale at $160/mg plus packing charges. 248Cm is available at a cost of $160/microgram, plus packing charges, from the O.R.N.L. Curium absorbed into the body accumulates in the bones, and is therefore very toxic as its radiation destroys the red-cell forming mechanism. The maximum permissible total body burden of 244Cm (soluble) in a human being is 0.3 microcurie. 1

Physical Properties

Melting Point:2*  1345 °C = 1618.15 K = 2453 °F
Boiling Point:2* 3100 °C = 3373.15 K = 5612 °F
Sublimation Point:2 
Triple Point:2 
Critical Point:2 
Density:3  13.51 g/cm3

* - at 1 atm

Electron Configuration

Electron Configuration:  *[Rn] 7s2 5f8
Block: f
Highest Occupied Energy Level: 7
Valence Electrons: 2

Quantum Numbers:

n = 5
ℓ = 3
m = -3
ms = -½

Bonding

Ionization Potential   eV 4  kJ/mol  
Ionization Potential   eV 4  kJ/mol  
Ionization Potential   eV 4  kJ/mol  
1 5.9915    578.1

Isotopes

Nuclide Mass 5 Half-Life 5 Nuclear Spin 5 Binding Energy
232Cm 1? min 0+
233Cm 233.05077(8) 1# min 3/2+# 1,758.93 MeV
234Cm 234.05016(2) 51(12) s 0+ 1,767.01 MeV
235Cm 235.05143(22)# 5# min 5/2+# 1,775.08 MeV
236Cm 236.05141(22)# 10# min 0+ 1,783.15 MeV
237Cm 237.05290(22)# 20# min 5/2+# 1,791.22 MeV
238Cm 238.05303(4) 2.4(1) h 0+ 1,799.29 MeV
239Cm 239.05496(11)# ~2.9 h (7/2-) 1,807.36 MeV
240Cm 240.0555295(25) 27(1) d 0+ 1,815.43 MeV
241Cm 241.0576530(23) 32.8(2) d 1/2+ 1,823.50 MeV
242Cm 242.0588358(20) 162.8(2) d 0+ 1,831.58 MeV
243Cm 243.0613891(22) 29.1(1) a 5/2+ 1,830.33 MeV
244Cm 244.0627526(20) 18.10(2) a 0+ 1,838.40 MeV
245Cm 245.0654912(22) 8.5(1)E+3 a 7/2+ 1,846.48 MeV
246Cm 246.0672237(22) 4.76(4)E+3 a 0+ 1,854.55 MeV
247Cm 247.070354(5) 1.56(5)E+7 a 9/2- 1,853.30 MeV
248Cm 248.072349(5) 3.48(6)E+5 a 0+ 1,861.37 MeV
249Cm 249.075953(5) 64.15(3) min 1/2(+) 1,869.45 MeV
250Cm 250.078357(12) 8300# a 0+ 1,877.52 MeV
251Cm 251.082285(24) 16.8(2) min (1/2+) 1,876.27 MeV
252Cm 252.08487(32)# <1 d 0+ 1,884.34 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. 5

Abundance

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 4:9-4:10.
(2) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:132.
(3) - Lide, David R. CRC Handbook of Chemistry and Physics, 84th ed.; CRC Press: Boca Raton, FL, 2002; p 4:39-4:96.
(4) - Dean, John A. Lange's Handbook of Chemistry, 11th ed.; McGraw-Hill Book Company: New York, NY, 1973; p 4:8-4:149.
(5) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 10:178 - 10:180.
(6) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:193, 12:219-220.
(7) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:123-6:137.
(8) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:107-6:122.
(9) - Atomic Mass Data Center. http://amdc.in2p3.fr/web/nubase_en.html (accessed July 14, 2009).