Barium
. Barium, symbol Ba, soft, silvery, highly reactive metallic element. Barium is in group 2 (or IIa) of the periodic table (see Periodic Law ) and is one of the alkaline earth metals . The atomic number of barium is 56. Barium was first recognized as an element in 1808 by the English scientist Sir Humphry Davy . The element reacts vigorously with water; it is rapidly corroded by moist air. In fact, the element is so reactive that it occurs in nature only as a compound. Its most important compounds are the minerals barium sulfate and barium carbonate (witherite) Barium is the 14th most common element, making up 1/2000th of the crust of the earth. The atomic weight of barium is 137.33. The element melts at about 725° C (about 1337° F), boils at about 1640° C (about 2984° F), and has a specific gravity of 3.5. Barium metal has few practical applications, although it is sometimes used in coating electrical conductors in electronic apparatus and in automobile ignition systems. Barium sulfat