It is a member of the actinide series in group IIIb of the periodic table . It is chemically reactive. It tarnishes in air, taking on a yellow cast when oxidized. It dissolves in hydrochloric, hydriodic, and perchloric acids and reacts with the halogens, carbon, nitrogen, and silicon. Plutonium, the second transuranium element , is named for Pluto, the second planet beyond Uranus.
Plutonium is found naturally in very small quantities in association with uranium ores.
However, it was discovered in 1940 at the Univ. Fifteen additional isotopes of plutonium are known. It is produced in large quantities in nuclear reactors from uranium-238, an abundant but nonfissionable isotope. Once begun, the reaction proceeds spontaneously until the uranium fuel rods in the reactor are converted to a certain uranium-plutonium mixture. The rods are dissolved in acid and the plutonium separated by chemical means, especially by solvent extraction.