Lanthanum (thing)

(So named (Greek lanthanein, "to be hidden") in 1839 by Karl Mosander, its discoverer, because it had been previously undetected in the mineral cerite) A soft, ductile, malleable, silvery chemical element, one of the rare-earth metals and the first member of the lanthanide series.

Symbol: La
Atomic number: 57
Atomic weight: 138.9055
Density (at room temperature and pressure): 6.15 g/cc
Melting point: 920°C
Boiling point: 3,464°C
Valence: +3
Ground state electron configuration: [Xe]5d¹6s²