Plutonium
. Plutonium, symbol Pu, radioactive metallic element that is used in nuclear reactors and nuclear weapons. The atomic number of plutonium is 94. The element is one of the transuranium elements in the actinide series of the periodic table . Isotopes of plutonium were first prepared by the American chemist Glenn T. Seaborg and his associates at the University of California at Berkeley in 1940. Trace amounts of the element have since been found in uranium ores, but plutonium is prepared in relatively large quantities today in nuclear reactors. Chemically, plutonium is reactive, its properties somewhat resembling those of the rare earth elements . The silvery metal, which becomes slightly yellow through oxidation caused by exposure to air, exists in six varying crystalline forms and has four different oxidation states. The metal gives off heat because of its radioactivity ; 15 different isotopes of plutonium, ranging in mass number from 232 to 246, are known. Plutonium melts at about 6...