Cerium is a Block F, Group 3, Period 6 element. The number of electrons in each of Cerium's shells is 2, 8, 18, 19, 9, 2 and its electronic configuration is [Xe]4f² 6s². 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 moderately toxic. 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 and moderately toxic. 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. In steel manufacturing it is used to remove free oxygen and sulfur by forming stable oxysulfides and by tying up undesirable trace elements, such as lead and antimony. It is considered to be the most efficient glass polishing agent for precision optical polishing. It is also used to decolor glass by keeping iron in its ferrous state. The ability of cerium-doped glass to block out ultra violet light is utilized in the manufacturing of medical glassware and aerospace windows. It is also used to prevent polymers from darkening in sunlight and to suppress discoloration of television glass. Cerium was first discovered by W. von Hisinger in 1903. The element was named after the asteroid Ceres. See Cerium research below.

Selenium is a Block P, Group 16, Period 4 element. The number of electrons in each of Selenium's shells is 2, 8, 18, 6 and its electronic configuration is [Ar] 3d¹⁰ 4s² 4p⁴. In its elemental form selenium's CAS number is 7782-49-2. The selenium atom has a radius of 116.pm and it's Van der Waals radius is 190.pm. The EPA does not classify selenium as carcinogenic, although selenium sulfide is a probable carcinogen. Selenates and selenites which are compounds of selenium, are highly toxic. Hydrogen selenide gas (SeH2) is the most acutely toxic compound of selenium. Selenium exhibits both photovoltaic action, where light is converted directly into electricity, and photoconductive action, where the electrical resistance decreases with increased illumination. of photocells and exposure meters for photographic use, as well as solar cells. Below its melting point, selenium is a p-type semiconductor and has many uses in electronic and solid-state applications. Selenium is available as metal and compounds with purities from 99% to 99.9999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. Selenium was first discovered by Jons Berzelius in 1817. The origin of the name Selenium comes from the Greek word "Selênê" meaning moon. See selenium research below.