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
2 Pallas Mars. The "Dawn" team was granted viewing time on the Hubble Space Telescope in September 2007 for a once-in-twenty-year opportunity to view Pallas at closest approach, to obtain comparative data for Ceres and Vesta. 2 Pallas is named after Pallas Athena (Ancient Greek: ), an alternate name for the goddess Athena. In some mythologies Athena killed Pallas, then adopted her friend's name out of mourning. "Pallas" is a Greek name and some other languages use variant versions of it for the asteroid: in Italian, "Pallade", Russian "Pallada", Spanish "Palas", and Arabic "Bālās", for example. In Chinese, however, the asteroid has