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silvery gray
General properties
Name, symbol, number barium, Ba, 56
Pronunciation /ˈbɛəriəm/ BAIR-ee-əm
Element category alkaline earth metals
Group, period, block 26, s
Standard atomic weight 137.327 g/mol
Electron configuration [Xe] 6s2
Electrons per shell 2, 8, 18, 18, 8, 2 (Image)
Physical properties
Phase solid
Density (near r.t.) 3.51 g/cm3
Liquid density at m.p. 3.338 g/cm3
Melting point 1000 K, 727 °C, 1341 °F
Boiling point 2170 K, 1897 °C, 3447 °F
Heat of fusion 7.12 kJ/mol
Heat of vaporization 140.3 kJ/mol
Specific heat capacity (25 °C) 28.07 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 911 1038 1185 1388 1686 2170
Atomic properties
Oxidation states +2
(strongly basic oxide)
Electronegativity 0.89 (Pauling scale)
Ionization energies 1st: 502.9 kJ/mol
2nd: 965.2 kJ/mol
3rd: 3600 kJ/mol
Atomic radius 222 pm
Covalent radius 215±11 pm
Van der Waals radius 268 pm
Crystal structure body-centered cubic
Magnetic ordering paramagnetic
Electrical resistivity (20 °C) 332 nΩ·m
Thermal conductivity (300 K) 18.4 W/(m·K)
Thermal expansion (25 °C) 20.6 µm/(m·K)
Speed of sound (thin rod) (20 °C) 1620 m/s
Young's modulus 13 GPa
Shear modulus 4.9 GPa
Bulk modulus 9.6 GPa
Mohs hardness 1.25
CAS registry number 7440-39-3
Most stable isotopes
Main article: Isotopes of barium
iso NA half-life DM DE (MeV) DP
130Ba 0.106% (0.5–2.7)×1021 y εε 2.620 130Xe
132Ba 0.101% >3×1020 y β+β+ 0.846 132Xe
133Ba syn 10.51 y ε 0.517 133Cs
134Ba 2.417% 134Ba is stable with 78 neutrons
135Ba 6.592% 135Ba is stable with 79 neutrons
136Ba 7.854% 136Ba is stable with 80 neutrons
137Ba 11.23% 137Ba is stable with 81 neutrons
138Ba 71.7% 138Ba is stable with 82 neutrons
Corroded barium metal

Barium is chemical element 56 on the periodic table. Its symbol is Ba. It contains 56 protons and 56 electrons. Its mass number is about 137.3. It is a metal.

Properties[change | change source]

Physical properties[change | change source]

Barium is part of a group of elements known as the alkaline earth metals. It is a silvery metal that easily turns black. It is soft and ductile. It can form alloys with some metals that are partially alloys and partially chemical compounds.

Chemical properties[change | change source]

Barium is reactive, and if you put pure barium metal in the air, it will react with oxygen. At first it will turn black, then white as barium oxide is formed. Barium reacts with water to make barium hydroxide and hydrogen gas. Barium also reacts very fast with acids to make a barium salt and hydrogen. Barium can form barium peroxide if it is burned in air.

Barium reacts with many other metal oxides and sulfides to make barium oxide or sulfide and the metal. It also reacts with carbon and nitrogen at a high temperature to make barium cyanide.

Chemical compounds[change | change source]

See also: Category:Barium compounds

Barium is too reactive as a metal, so it is not found in the earth as a metal. It is found in chemical compounds. Barium only occurs in one oxidation state: +2. Most barium compounds are colorless. The ones that dissolve in water or stomach acid are very toxic. Barium sulfate is well known because it does not dissolve in water or acids. Barium compounds are quite heavy. Barium compounds put out a greenish flame when heated red-hot.

Occurrence[change | change source]

Barium sulfate as barite

Barium is found as barium sulfate (barite) and barium carbonate (witherite) in the ground. Both of these minerals do not dissolve in water. Barium sulfate hardly dissolves in anything. Barium is found mainly in China, Germany, India, Morocco, and the US.

Preparation[change | change source]

It is very hard to get barium from barium sulfate. So barium sulfate is reduced by carbon to make barium sulfide and carbon dioxide. The barium sulfide is dissolved in hydrochloric acid. This makes hydrogen sulfide and barium chloride. The barium chloride is melted and electrolyzed to get liquid barium metal. The barium metal is solidified and stored in oil.

Barium carbonate, the other ore of barium, is dissolved in hydrochloric acid to make barium chloride and carbon dioxide. The barium chloride is melted and electrolyzed, making barium metal.

Uses[change | change source]

As a metal[change | change source]

Barium is used to remove oxygen from cathode ray tubes and vacuum tubes. It is placed inside and reacts with all of the oxygen, using it up. Barium is also used in spark plug wire.

As chemical compounds[change | change source]

Certain compounds of barium, such as barium sulfate, are not toxic and can be put in the body. We can see where the barium travels in the body by X-rays and this can tell us whether there are problems, such as blockages. The barium sulfate builds up inside the body accumulating in organ systems. Barium sulfate absorbs the X-Rays as they pass through the body and an image is formed from the points where the rays have not passed through. It is useful because it provides a reasonably detailed image from very limited radiation exposure, compared with a CT scan for instance. Barium sulfate can be used as a pigment, too.

Other barium compounds have several other uses.

Safety[change | change source]

Barium is a very toxic element, though, and is dangerous. There is a really small amount of barium in our food, and this does not cause problems. If we get barium from other places, though, it can cause many problems. Even 1 gram of barium can kill you. It is dangerous because it acts like other really important elements, such as calcium and magnesium. If barium replaces these elements, it messes up the body.