BARIUM (REVISED)

Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.

Overview

Barium was first isolated in 1808 by English chemist Sir Humphry Davy (1778-1829). In 1807 and 1808, Davy also discovered five other new elements: sodium, potassium, strontium, calcium, and magnesium. All of these elements had been recognized much earlier as new substances, but Davy was the first to prepare them in pure form. (See sidebar on Davy in the Calcium entry.)

Barium had first been identified as a new material in 1774 by Swedish chemist Carl Wilhelm Scheele (1742-86). The form with which Scheele worked, however, was a compound of barium, barium sulfate (BaSO₄). Barium sulfate is, in fact, the most common naturally occurring ore of barium. It is generally known as barite or barytes.

SYMBOL
Ba

ATOMIC NUMBER
56

ATOMIC MASS
137.34

FAMILY
Group 2 (IIA)
Alkaline earth metal

PRONUNCIATION
BARE-ee-um

Barium is a member of the alkaline earth metals. The alkaline earth metals make up Group 2 (IIA) of the periodic table. The other elements in this group are beryllium, magnesium, calcium, strontium, and radium. These elements tend to be relatively active chemically and form a number of important and useful compounds. They also tend to occur abundantly in the Earth's crust in a number of familiar minerals such as aragonite, calcite, chalk, Limestone, marble, travertine, magnesite, and dolomite. Alkaline earth compounds are widely used as building materials.

Barium itself tends to have relatively few commercial uses. However, its compounds have a wide variety of applications in industry and medicine. Barium sulfate is used in X-ray studies of the gastrointestinal (GI) system. The GI system includes the stomach, intestines, and associated organs.

Discovery and naming

The first mention of barium compounds goes back to the early seventeenth century. Early records mention a "Bologna stone," named for the the city of Bologna, Italy. The Bologna stone glowed in the dark.

For more than a hundred years, researchers labored without being able to identify the elements in the stone. In 1774, Scheele announced the presence of a new element in the Bologna stone. Today, scientists know that the stone was a form of barite. Five years later, Scheele demonstrated that barite was also present in heavy spar. This dense transparent mineral closely resembles ordinary spar, a compound of calcium.

Physical properties

Pure barium is a pale yellow, somewhat shiny, somewhat malleable metal. Malleable means capable of being hammered into thin sheets. It has a melting point of about 700°C (1,300°F) and a boiling point of about 1,500°C (2,700°F). Its density is 3.6 grams per cubic centimeter.

When heated, barium compounds give off a pale yellow-green flame. This property is used as a test for barium.

Chemical properties

Barium is an active metal. It combines easily with oxygen, the halogens, and other non-metals. The halogens are Group 17 (VIIA) of the periodic table and include fluorine, chlorine, bromine, iodine, and astatine. Barium also reacts with water and with most acids. It is so reactive that it must be stored under kerosene, petroleum, or some other oily liquid to prevent it from reacting with oxygen and moisture in the air. Of the alkaline family, only radium is more reactive.

Occurrence in nature

Barium is the fourteenth most abundant element in the Earth's crust. Its abundance is estimated to be about 0.05 percent.

The most common sources of barium are barite and witherite. Witherite is an ore containing barium carbonate (BaCO₃). The world's major sources of barium ores are China, India, Morocco, the United States, Turkey, and Kazakhstan. Most of the barium processed in the United States comes from Louisiana, Nevada, and Texas.

Isotopes

There are seven naturally occurring isotopes of barium: barium-130, barium-132, barium-134, barium-135, barium-136, barium-137, and barium-138. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

About a dozen radioactive isotopes of barium are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.

None of the isotopes of barium has any practical commercial application.

Extraction

Pure barium is produced by reacting barium oxide (BaO) with aluminum or silicon:

Uses

Barium metal has relatively few uses because it is so active. This activity makes it an excellent "getter" or "scavenger" when removing unwanted oxygen from sealed glass containers. (Oxygen can interfere with the operation of a vacuum tube, for example.) By adding a small amount of barium to the tube, the free oxygen inside will be "soaked up." The oxygen reacts with the barium to form barium oxide.

Compounds

Compounds of barium, especially barite (BaSO₄), are critical to the petroleum industry. Barite is used as a weighting agent in drilling new oil wells. A weighting agent is a material that adds body to petroleum.

Drilling for oil used to produce huge gushers. A gusher is an oil that sprays out of the well into the air. Gushers are undesirable, because they waste oil and can burn for months if ignited.

Gushers are caused by the pressure of oil rushing into a newly drilled hole in the ground. This pressure pushes the oil upward much too rapidly. Barite is added to the hole as it is drilled. There, it tends to mix with oil in the ground and form a very dense mixture that comes out much more slowly and under control.

Ninety percent of the barite mined in the United States is used by the petroleum industry. Here are other uses of barite and other barium compounds:

Taking a look inside the body

P erhaps the best known use of barium compounds is in medicine. Doctors often want to know what is happening inside a patient's body. One way to find out, of course, is through surgery. But surgery is a drastic procedure. It can cause new problems for the patient. As a result, medical researchers have developed procedures that are less extreme. One such method is called radiography.

Radiography is a technique in which X rays are passed through the body. X rays are high energy light waves. They can pass through skin and tissue, but are absorbed by bones. So X rays are a good way of finding out if a bone is broken, for example.

Any type of light appearing on film from an X ray produces a black area, or exposure. The X rays pass through soft issues, exposing the film. Bones look greyish white on the film, depending on how much energy gets through.

Radiography can be also be used for studying parts of the body where bones are not involved. For example, a doctor might want to study a person's stomach. Since there are no bones in the stomach, some other method must be used to see inside the stomach.

Barium sulfate is often used in such cases. Barium sulfate has some of the same properties as bony material. Therefore, since X rays will not pass through barium sulfate, this compound can be used to examine certain soft tissues.

Radiography using barium sulfate is called a barium swallow or a barium enema. Barium sulfate is mixed with water into a slurry (mixture) that looks and tastes like ground-up chalk. The patient swallows the dense mixture. A doctor or nurse then holds a fluoroscope over the patient's abdomen. The fluoroscope emits X rays that show up on a television screen.

The barium sulfate-water mixture slowly travels down the patient's throat, into the stomach, through the intestines, and out through the bowels. As the barium sulfate coats the lining of the digestive tract, a doctor can see if anything is wrong.

How can a toxic compound like barium sulfate be used for this procedure? Barium sulfate does not dissolve in water. So it cannot enter the blood stream. If it cannot get into the blood, it has no toxic effects. The barium sulfate is eliminated through the bowels a few hours after the procedure.

barium sulfate (barite): used to add body to or as a coating for paper products; as a white coloring agent in paints, inks, plastics, and textiles; in the manufacture of rubber products; in the production of batteries; in medical applications (see accompanying sidebar)

barium carbonate (BaCO₃): used in the production of chlorine and sodium hydroxide; as rat poison; in special types of glass

barium oxide (BaO): used to remove water from solvents; in the petroleum industry

barium nitrate (Ba(NO₃)₂): used in fireworks; as rat poison; in special ceramic glazes

Health effects

Barium and all of its compounds are very toxic.

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.

Barium

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 doesn't 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 naturally occur 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 (Ba) 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.

During the 1700s, chemists thought that barium oxide and calcium oxide were the same substance. In 1774, Carl Wilhelm Scheele showed that barium oxide is a distinct compound, pointing the way toward discovery of the element. In the early 1800s, after electric batteries had been invented, chemists began using electric currents to break compounds apart. Humphry Davy, 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.

Barium

Pure barium is rarely used outside the laboratory. Barium compounds are found primarily in two ores (minerals from which valuable substances, like metal, can be removed). The first ore is barite and the second is witherite. Barite contains a sulfate (a salt of sulfuric acid) compound while witherite contains barium carbonate (a salt of carbonic acid). While barium and all of its soluble (dissolvable) compounds are poisonous, barium sulfate is used in medical procedures because it will not dissolve in water or other body fluids.

Like other metals, barium is a good conductor of heat and electricity. It is silver and white in color and relatively malleable (flexible). Chemically, it resembles calcium and strontium, fellow members of the alkaline-earth family of metals. Barium gets its name from the Greek word for barys, which means "heavy."

During the 1700s, chemists thought that barium oxide and calcium oxide were the same substance. In 1774, Carl Wilhelm Scheele showed that barium oxide is a distinct compound. After electric batteries were invented in the 1800s, chemists began using electric currents to break compounds apart. Humphry Davy, who pioneered this technique, later called electrolysis, discovered barium in 1808. Davy produced barium 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.

Barium and Medicine

Barium's many compounds have a number of practical applications. Perhaps the most familiar is the one used in a medical procedure, 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.

Industrial Uses

Barium also has many industrial applications. 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. The sulfate is also an ingredient in oildrilling "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.

Barium

melting point: 729°C
boiling point: 1,640°C
density: 3.51 g/cm³
most common ions: Ba²⁺

The fifty-sixth element in the Periodic Table, barium has been known in various mineral forms since the 1600s. However, it was not until the 1770s that Carl W. Scheele and J. G. Gahn independently began separating barium compounds from other components of various minerals, isolating barium oxide (BaO) and barium sulfide (BaSO₄). The latter compound was isolated from the heavy feldspar and eventually named barite, from the Greek word barys, meaning "heavy." It was not until 1808 that elemental barium was isolated by Sir Humphry Davy, using his famous electrolysis system.

In its elemental form, barium is a relatively soft, silvery-white metal . As a highly reactive member of the alkaline-earth family, metallic barium will oxidize readily in water to form barium hydroxide, evolving hydrogen gas. It will also react readily and vigorously with oxygen in air to form BaO. As with other alkaline-earth elements, barium's most common oxidation state is +2.

As the fourteenth most abundant element in Earth's crust, barium is the most common of all elements with an atomic number greater than 26 (iron). Barium and its compounds are used in a variety of ways, including in electronics, fireworks (where barium burns with its well-known yellow-green flame), paint pigments, and insecticides. Although barium compounds are highly toxic, doctors sometimes have patients ingest a special barium sulfate solution when it is necessary to x-ray their digestive tracts. The BaSO₄ is insoluble enough that it is not absorbed and so passes through the body without causing harm. In the process, the BaSO₄ can deflect X rays, thus making it possible to clearly image the soft tissue of the digestive tract.

see also Alkaline Earth Metals; Davy, Humphry; Scheele, Carl.

David A. Dobberpuhl

Bibliography

Heiserman, David L. (1992). Exploring Chemical Elements and Their Compounds. Blue Ridge Summit, PA: Tab Books.

Krebs, Robert E. (1998). The History and Use of Our Earth's Chemical Elements: A Reference Guide. Westport, CT: Greenwood Press.