lanthanum

Lanthanum is a chemical element; it has symbol La and atomic number??57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the first and the prototype of the lanthanide series, a group of 15??similar elements between lanthanum and lutetium in the periodic table. Lanthanum is traditionally counted among the rare-earth elements. Like most other rare-earth elements, its usual oxidation state is +3, although some compounds are known with an oxidation state of +2. Lanthanum has no biological role in humans but is used by some bacteria. It is not particularly toxic to humans but does show some antimicrobial activity.