Rare Earths | AMERICAN ELEMENTS
Rare Earth Elements. Cerium is the most abundant of the rare earths. It is characterized chemically by having two valence states, the +3 cerous and +4 ceric states. The ceric state is the only nontrivalent rare earth ion stable in aqueous solutions, making it strongly acidic and moderately toxic, as well as a strong cerous state closely resembles the other trivalent rare earths.