Barium – facts and properties

Position in the periodic table

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Occurrence and extraction

Barium occurs in nature only in compounds. The most common mineral is barite, also called heavy spar, a sulfate with the formula BaSO₄. For a pale mineral its density is strikingly high, which gave it its name. Less common is witherite, BaCO₃. Major producers of barite are China, India and Morocco. In Germany barite is still mined in the Black Forest and was formerly mined in the Harz.

Most barite is used as the mineral. The metal itself is made only in small amounts, for example by reducing barium oxide with aluminium under vacuum.

As an element, barium was first prepared in 1808 by the English chemist Humphry Davy. He split moist barium compounds with an electric current, using mercury as an aid. Decades earlier, the Swedish chemist Carl Wilhelm Scheele had recognised a new earth, barium oxide, in heavy spar.

Properties and reactions

Barium is in period 6 and group 2, below strontium and above radium. In the period, caesium lies to its left. Its electron configuration is [Xe] 6s² and its electronegativity is 0.89. The element has 2 valence electrons. The metal has a density of 3.62 g/cm³, melts at 727 °C and boils at 1897 °C. It is soft and tarnishes quickly in air.

Barium is one of the most reactive of the stable alkaline earth metals. It reacts with water, forming hydrogen and barium hydroxide, and is therefore stored under oil or protective gas. In compounds it almost always occurs as a doubly charged positive ion. In a flame, barium compounds give a green colour. The solubility of the sulfates falls down the group, and barium sulfate is practically insoluble. A classic analytical test for sulfate relies on this: barium ions precipitate white barium sulfate from sulfate solutions.

This very difference decides how toxic the compounds are. Soluble barium salts such as the chloride and the nitrate are poisonous. The carbonate is also dangerous because it dissolves in stomach acid. Barium ions disturb the working of muscles and the heart, causing cramps, irregular heartbeat and paralysis. Barium sulfate, in contrast, hardly dissolves and is not absorbed by the body. Soluble barium salts are toxic; schools handle them only under strict rules.

Uses in everyday life and technology

Most barite is used in deep drilling. Ground barite is mixed into the drilling fluid and makes it heavy. The pressure of the fluid then holds back the gas and oil in the rock and keeps the borehole stable.

In medicine, barium sulfate is an X-ray contrast agent. Because barium absorbs X-rays strongly, a contrast meal that the patient drinks outlines the oesophagus, stomach and intestine on the image. The agent is made in high purity so that it contains no soluble barium salts, and it is excreted after the examination.

In fireworks, barium salts such as barium nitrate supply the green colour. A rich green also needs a chlorine-containing compound in the mix. Barium sulfate is also used as a white filler and pigment in paints, varnishes and paper.

In technology, barium titanate is found in ceramic capacitors and in components that turn mechanical pressure into voltage. Barium contributes to special glasses, and barite aggregate in heavy concrete shields against radiation. With yttrium, copper and oxygen it forms the high-temperature superconductor YBCO.

Because soluble salts are toxic, their production, handling and disposal are subject to legal rules.

Molecules containing this element

• Barium sulfide BaSView in 3D
• Barium oxide BaOView in 3D
• Barium chloride BaCl₂View in 3D

Quick question

What is the atomic number of barium (Ba)?

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