A rare, silver-white, ductile, malleable chemical element, one of the platinum metals. At room temperature, it has the unusual property of absorbing up to nine hundred times its own volume in hydrogen, possibly forming Pd2H, although it is not yet clear if this is a true compound. Palladium is found with deposits of platinum and other members of the platinum metals in Russia, North America, South America, Ethiopia, and Australia; and with nickel-copper deposits in South Africa and Ontario, Canada.
Palladium is used as a catalyst, especially in hydrogenation and dehydrogenation processes. Hydrogen readily diffuses through heated palladium; this provides a mean of purifying hydrogen gas. As an alloy with gold, silver, and other metals, palladium is used in jewelry, watchmaking, dentistry, and in making surgical instruments and electrical contacts. White gold is an alloy of gold decolorized by the addition of palladium. The radioactive isotope Palladium-103 has been effective in treating prostate cancer, by inhibiting the growth of tumors.
Symbol: Pd
Atomic number: 46
Atomic weight: 106.42
Density (at room temperature and pressure): 12.02 g/cm3
Melting point: 1,552°C
Boiling point: 2,963°C
Main valence: +2
Ground state electron configuration: [Kr]4d10
Palladium was discovered in 1803 by William Hyde Wollaston, English chemist, in London, England, in crude platinum ore from South America, who named it after the recently discovered asteroid Pallas. He dissolved the ore in aqua regia, neutralized the acid with sodium hydroxide, and precipitated the platinum by treatment with ammonium chloride, as ammonium chloroplatinate. Palladium was then removed as palladium cyanide by treatment with mercuric cyanide. The metal was produced from this cyanide by heating.