Lanthanum

Lanthanum 138.9055(2)   La 57 1s22s22p63s23p63d10 4s24p64d105s25p65d16s2 [ ? ] Transition metal: Properties: Soft, silvery-white,malleable, ductile metal.

Lanthanum is a chemical element, having the chemical symbol La. Its atomic number (the number of protons) is 57. It has a standard atomic weight of 138.9055 g•mol ⁻¹ and is a solid in its elemental form.

Lanthanum is considered to be a member of the "Transition metal" class of elements. At a pressure of 101.325 kPa, it has a boiling point of 3,464 °C and a melting point of 920 °C.

A white, soft element, lanthanum is classified in a number of different "categories" of elements. In addition to being a transition metal, it belongs to the "rare earth metals", (which include scandium, yttrium, and actinium), and is also the namesake of the "lanthanides", a group of elements in the periodic table having atomic numbers from 57 (lanthinide itself) to 71 (lutetium).