Scandium(III) and yttrium(III)

Abstract According to the inorganic chemistry text book written by Cotton and Wilkinson, scandium is not truly a rare earth element but yttrium and lanthanides are rare earth elements. The stable oxidation state of scandium is trivalent and the ionic radius of scandium (III) is significantly smaller (0.89 Å) than those for any of the rare earth elements (1.0-1.17 Å). Chemical behaviour is intermediate between aluminium and that of lanthanides. Yttrium has a trivalent oxidation state similar to scandium and lanthanide elements and the ionic radius of yttrium (III) (1.04 Å) is close to those of erbium (1.03 A) and holmium (1.04