Lanthanum
131lanthanide contraction — ▪ chemistry also called lanthanoid contraction in chemistry, the steady decrease in the size of the atoms and ions of the rare earth elements (rare earth element) with increasing atomic number from lanthanum (atomic number 57) through… …
132lanthanide — noun Any of the 14 rare earth elements from cerium (or from lanthanum) to lutetium in the periodic table; because their outermost orbitals are empty, they have very similar chemistry; below them are the actinides. Syn: lanthanate …
