Period 5 element and because of its rarity, rhodium is usually alloyed with platinum or palladium and applied in high-temperature and corrosion-resistive coatings. White gold is often plated with a thin rhodium layer to improve its optical impression while sterling silver is often rhodium plated for tarnish resistance. Rhodium detectors are used in nuclear reactors to measure the neutron flux level. Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named
Group 3 element salts, he named it from the Ancient Greek "λανθάνειν" [lanthanein] (lit. "to lie hidden"). Relatively pure lanthanum metal was first isolated in 1923. Lutetium was independently discovered in 1907 by French scientist Georges Urbain, Austrian mineralogist Baron Carl Auer von Welsbach, and American chemist Charles James as an impurity in the mineral ytterbia, which was thought by most chemists to consist entirely of ytterbium. Welsbach proposed the names "cassiopeium" for element 71 (after the constellation Cassiopeia) and "aldebaranium" (after the star Aldebaran) for the new name of ytterbium but these naming proposals were rejected, although many German scientists in the