Yttrium, Lanthanum, and the Lanthanide Elements *

The chemistry of yttrium, lanthanum, and the lanthanide elements is, both in solids and in solution, primarily that of a group of classical tripositive ions. The stability of the +3 state for yttrium, lanthanum, and lutetium is obvious, since the energetics for oxidation and reduction of the completed - subshell +3 ions are unfavorable. The chemistry of yttrium is that of a classical trivalent element. Most of its properties are those of a highly electropositive metal which is thermodynamically unstable with respect to its trivalent ion in aqueous solution. Lanthanum is more electropositive than any of the lanthanides. In basic solution, however, the heavy lanthanides are more electropositive than lanthanum because of the lower solubility of their hydroxides. The predominant stability of the +3 ions for the lanthanides cerium through ytterbium is striking, and the explanation for this stability is somewhat more subtle.