Curium

General

Name	Curium	Symbol	Cm
Atomic number	96	Atomic weight	(247)
Density @ 293 K	13.5 g/cm3	Atomic volume	18.28 cm3/mol
Group	Rare Earth, Actinides	Discovered	1944

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States

State (s, l, g)	s
Melting point	1613.2 K	Boiling point	K
Heat of fusion	15.0 kJ/mol	Heat of vaporization	?

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Energies

1st ionization energy	581 kJ/mole	Electronegativity	1.3
2nd ionization energy	kJ/mole	Electron affinity	kJ/mole
3rd ionization energy	kJ/mole	Specific heat	?
Heat atomization	kJ/mole atoms

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Oxidation & Electrons

Shells	2,8,18,32,25,9,2	Electron configuration	[Rn] 5f7 6d1 7s2
Minimum oxidation number	0	Maximum oxidation number	4
Minimum common oxidation number	0	Maximum common oxidation number	3

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Appearance & Characteristics

Structure	fcc: face-centered cubic	Color	silvery-white
Uses	thermoelec. pwr, n source	Toxicity
Hardness	mohs	Characteristics	Radioactive

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Reactions

Reaction with air			Reaction with 6M HCl
Reaction with 6M HCl			Reaction with 15M HNO3
Reaction with 6M NaOH

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Other Forms

Number of isotopes		0	Hydride(s)		CmH2
Oxide(s)		CmO Cm2O3 CmO2	Chloride(s)		CmCl3

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Radius

Ionic radius (2- ion)	pm	Ionic radius (1- ion)	pm
Atomic radius	174 pm	Ionic radius (1+ ion)	pm
Ionic radius (2+ ion)	pm	Ionic radius (3+ ion)	111 pm

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Conductivity

Thermal conductivity		J/m-sec-deg	Electrical conductivity		1/mohm-cm
Polarizability		23 A^3

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HOME

Source	Synthetic	Rel. abund. solar system	log
Abundance earth's crust	log	Cost, pure	$/100g
Cost, bulk	$/100g

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History:

(Pierre and Marie Curie) 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 (30Mg) 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. Fourteen 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 rare earth homolog, but it has a more complex crystal structure. Curium is silver in color, is chemically reactive, and is more electropositive than aluminum. Most compounds of trivalent curium are faintly yellow in color. 242 Cm 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 $100/mg. 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 microcure.

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