Lanthanum is a soft, ductile, silvery-white metallic chemical element with symbol La and atomic number 57. It tarnishes rapidly when exposed to air and is soft enough to be cut with a knife. It gave its name to the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table: it is also sometimes considered the first element of the 6th-period transition metals. As such, it almost always assumes the oxidation state +3. Lanthanum has no biological role and is not very toxic.