Rare Earth Elements
, Rare Earth Elements, series of chemical elements of the periodic table. The rare earth elements (or rare earth metals) include the elements with atomic numbers 57 through 71, and, named in order, are lanthanum , cerium , praseodymium , neodymium , promethium , samarium , europium , gadolinium , terbium , dysprosium , holmium , erbium , thulium , ytterbium , and lutetium . Yttrium (atomic no. 39) and scandium (atomic no. 21) are sometimes included in the group of rare earth elements. The elements cerium (atomic no. 58) through lutetium (atomic no. 71) are commonly known as the lanthanide series . PROPERTIES Chemically, most of the rare earth elements are trivalent (see Valence ). Cerium alone forms compounds with a valence of +4. Most rare earth compounds are strongly paramagnetic. An alloy composed of iron and of rare earth metals, called misch metal, is pyrophoric. When scratched it gives off sparks capable of igniting flammable gases. It is used in cigarette lighters, miners'