(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