Barium

Barium—a soft, silvery very reactive metallic element—is the fifth element in Group 2 of the periodic table, the alkaline earth elements. It has an atomic number of 56, atomic mass of 137.327, and chemical symbol of Ba.

Although pure barium is rarely used outside the laboratory, barium’s many compounds have a number of practical applications. Perhaps the most familiar is the barium enema. When doctors need to examine a patient’s digestive system, a mixture containing barium sulfate is used to coat the inner lining of the intestines. Similarly, to enhance examination of the stomach and esophagus, the patient drinks a chalky barium sulfate liquid. When the patient is x rayed, the barium coating inside the digestive tract absorbs a large proportion of the radiation. This highlights the black-and-white contrast of the x-ray photograph, so that doctors can better diagnose digestive problems.

Barium sulfate (BaSO₄) is safe to use for this purpose because it does not dissolve in water or other body fluids. However, barium and all of its soluble compounds are poisonous. Because pure barium reacts immediately with oxygen and water vapor to produce barium oxide when exposed to air, barium does not occur naturally in an uncombined state. Barium compounds are found primarily in two mineral ores: barite, which contains the sulfate compound, and witherite, which contains barium carbonate.

Like other metals, barium is a good conductor of heat and electricity. It is silvery white and relatively malleable. Chemically, it resembles calcium and strontium, which are fellow members of the alkaline-earth family of metals. The metal gets its name from the Greek word for heavy, barys, which was first used to name the mineral barite, or heavy spar. Barium’s atomic number is 56 and it has seven stable isotopes.

The first mention of barium compounds goes back to the early seventeenth century when records spoke of a Bologna stone, named for the city of Bologna, Italy. The Bologna stone attracted the attention of scholars because it glowed in the dark. For more than a century, researchers attempted to discover the composition of the Bologna stone. During the eighteenth century, chemists thought that barium oxide and calcium oxide were the same substance. In 1774, Swedish chemist Carl Wilhelm Scheele (1742–1786) showed that barium oxide is a distinct compound. Further, Scheele announced that he had found a new element in the Bologna stone. He suggested the name barium for the element based on the scientific name for the Bologna stone, barite. In the early 1800s, after electric batteries had been invented, chemists began using electric currents to break compounds apart. English chemist Sir Humphry Davy (1778–1829), who pioneered this technique of electrolysis, discovered barium in 1808. Davy produced the metal for the first time by passing an electric current through molten barium hydroxide. He also used electrolysis to isolate potassium, sodium, calcium, magnesium, and strontium.

Although pure barium metal can be used to remove undesirable gases from electronic vacuum tubes, barium’s compounds are much more important to industry. Barium sulfate is a component of lithopone, a white pigment used in paints. Barium carbonate is used in the production of optical glass, ceramics, glazed pottery, and specialty glassware; it is also an ingredient in oil drilling muds or slurries that lubricate the drill bit. The bright yellow-green colors in fireworks and flares come from barium nitrate. Motor oil detergents, which keep engines clean, contain barium oxide and barium hydroxide.