CURIUM

(Cm), synthetic chemical element of the actinide series in Group IIIb of the periodic table, atomic number 96. Undetected in nature, curium (as the isotope curium-242) was discovered (summer 1944) at the University of Chicago by Glenn T. Seaborg, Ralph A. James, and Albert Ghiorso in a plutonium isotope, plutonium-239, that had been bombarded by helium ions (alpha particles) in the 60-inch cyclotron at the University of California, Berkeley. It was the third transuranium element to be discovered. Curium is a silvery metal. All of its isotopes are radioactive. For chemical research curium-242 (163-day half-life) has been supplanted by curium-244 (17.6-year half-life) and the still longer-lived isotopes from curium-245 to curium-248, all of which are built up from plutonium-239 by neutron irradiation. Curium exhibits its common +3 oxidation state as the very faint yellow Cm3+ ion in aqueous solution, as the sesquioxide Cm2O3, and as the trihalides; it is chemically similar to the other tripositive actinide elements and to the lanthanide elements. The +4 oxidation state appears in the black dioxide CmO2 and as the Cm4+ ion complexed with the fluoride ion. The isotopes curium-242 and curium-244 are well suited for use in space because they can provide compact, long-lived sources of electricity through conversion of their heat of radioactive decay by thermoelectric and thermionic devices. atomic number 96 stablest isotope 247 melting point c. 1,340 C (2,444 F) specific gravity c. 13.51 valence 3,4 electronic config. 2-8-18-32-25-9-2 or (Rn)5f 76d17s2