WRITTEN BYLester MorssAdjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland.See Article History
Alternative Title: Cm
Curium (Cm), synthetic chemical element of the actinoid series of the periodic table, atomic number 96. Unknown in nature, curium (as the isotope curium-242) was discovered (summer 1944) at the University of Chicago by American chemists Glenn T. Seaborg, Ralph A. James, and Albert Ghiorso in a sample of a plutonium isotope, plutonium-239, that had been bombarded by helium ions (alpha particles) in the 152-cm (60-inch) cyclotron at the University of California, Berkeley. It was the third transuranium element to be discovered. The element was named after French physicists Pierre and Marie Curie.
BRITANNICA QUIZ118 Names and Symbols of the Periodic Table QuizTs
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 (18.1-year half-life) and the still longer-lived isotope curium-248, 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 actinoid elements and to the lanthanoid elements. The +4 oxidation state appears in the black dioxide CmO2 and as the Cm4+ ion complexed with the fluoride ion.
| atomic number | 96 |
|---|---|
| stablest isotope | 247 |
| melting point | about 1,340 °C (2,444 °F) |
| specific gravity | about 13.51 |
| oxidation states | +3, +4 |
| electron configuration of gaseous atomic state | [Rn]5f 76d17s2 |
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