lanthanide series

lanthanide series a series of metallic elements, included in the rare-earth metals , in Group 3 of the periodic table . Members of the series are often called lanthanides, although lanthanum (atomic number 57) is not always considered a member of the series. The series always includes the 14 elements with atomic numbers 58 through 71, which are (in order of increasing atomic number) cerium , praseodymium , neodymium , promethium , samarium , europium , gadolinium , terbium , dysprosium , holmium , erbium , thulium , ytterbium , and lutetium . All of the members of the series very closely resemble lanthanum and one another in their chemical and physical properties; as the atomic number increases in this series, added electrons enter the 4f electron orbital. Chemically, they are about as reactive as calcium. They all form trivalent compounds; some also form divalent or tetravalent compounds. The lanthanides have similiar sizes so that any given compound of the rare earths is likely to crystallize with the same structure as any other rare earth; however, the lattice parameters become smaller and the crystal denser as compounds proceed across the series.

lanthanide series (lanthanide elements, rare-earth metals) Series of 15 rare metallic elements with atomic numbers from 57 to 71. They are, in order of increasing atomic numbers: lanthanum (sometimes not considered a member), cerium, praseodymium, neodymium, promethium (the only radioactive member), samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Their properties are similar. The shiny metals occur in monazite and other rare minerals and are placed in group III of the periodic table. Each element is analogous to the corresponding radioactive actinide series.