Noun

1. 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.

Usage notes

• According to IUPAC - "Although lanthanoid means 'like lanthanum' and so should not include lanthanum, lanthanum has become included by common usage. Similarly, actinoid. The ending 'ide' normally indicates a negative ion, and therefore lanthanoid and actinoid are preferred to lanthanide and actinide. However, lanthanide and actinide are still allowed owing to wide current use."

Synonyms

• lanthanate (obsolete)
• lanthanoid (including lanthanum)
• lanthanon (proposed to avoid confusion with the usual meaning in chemistry of -ide)
• rare-earth element

See also

• cerium
• praseodymium
• neodymium
• promethium
• samarium
• europium
• gadolinium
• terbium
• dysprosium
• holmium
• erbium
• thulium
• ytterbium
• lutetium