Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


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 sulfate (BaSO4) is used as a filler for rubber products, in paint, and in linoleum. Barium nitrate is used in fireworks, and barium carbonate in rat poisons. A form of barium sulfate, which is opaque to X rays, is used for the X-ray examination of the gastrointestinal tract.