Cerium is a Block F, Group 3, Period 6 element. The electronic configuration is [Xe]4f²6s². In its elemental form cerium's CAS number is 7440-45-1. The cerium atom has a radius of 182.5.pm and it's Van der Waals radius is 181.pm. Cerium is one of the products manufactured and distributed under the tradename AE Rare Earths. Cerium is the most abundant of the rare earths 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. It is also a strong oxidizer. The cerous state closely resembles the other trivalent rare earths. The numerous commercial applications for cerium include metallurgy, glass and glass polishing, ceramics, catalysts, as the electrolyte for solid oxide fuel cells when doped with yttrium, gadolinium or samarium and in phosphors.