Tris(cyclopentadienyl)cerium

See more Cerium products. Cerium (atomic symbol: Ce, atomic number: 58) is a Block F, Group 3, Period 6 element with an atomic weight of 140.116. The number of electrons in each of cerium's shells is 2, 8, 18, 19, 9, 2 and its electron configuration is [Xe]4f² 6s². The cerium atom has a radius of 182.5 pm and a Van der Waals radius of 235 pm. In its elemental form, cerium has a silvery white appearance. Cerium is the most abundant of the rare earth metals. It is characterized chemically by having two valence states, the +3 cerous and +4 ceric states. The ceric state is the only non-trivalent rare earth ion stable in aqueous solutions. It is therefore strongly acidic and oxidizing, in addition to being moderately toxic.The cerous state closely resembles the other trivalent rare earths. Cerium is found in the minerals allanite, bastnasite, hydroxylbastnasite, monazite, rhabdophane, synchysite and zircon. Cerium was discovered by Martin Heinrich Klaproth, Jöns Jakob Berzelius, and Wilhelm Hisinger in 1803 and first isolated by Carl Gustaf Mosander in 1839. The element was named after the asteroid Ceres, which itself was named after the Roman god of agriculture.