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Barium                                    

Standard Sate: solid at 298k

Color: Silvery white                                                                                                                        

Barium is a metallic element, soft, and when pure is silvery white like lead. The metal
oxidises very easily and it reacts with water or alcohol. Barium is one of the
alkaline-earth metals. Small amounts of barium compounds are used in paints and
glasses.

(Ba), chemical element, one of the alkaline-earth metals of main
Group IIa of the periodic table. The element is used in metallurgy, and
its compounds in pyrotechnics, petroleum mining, and radiology.

Properties, occurrence, and uses. Barium, which is slightly harder
than lead, has a silvery white lustre when freshly cut. In nature it is
always found combined with other elements. The Swedish chemist
Carl Wilhelm Scheele discovered (1774) a new base (baryta, or
barium oxide) as a minor constituent in pyrolusite, and from this base
he prepared some crystals of barium sulfate, which he sent to Johan
Gottlieb Gahn, the discoverer of manganese. A month later Gahn
found that the mineral barite is also composed of barium sulfate.
Only after the electric battery became available could Sir Humphry
Davy finally isolate (1808) the element itself by electrolysis.

Though barium minerals are dense, barium itself is comparatively
light. Barium constitutes about 0.04 percent of the Earth's crust,
chiefly as the minerals barite and witherite. Commercial production of
barium depends upon the electrolysis of fused barium chloride or the
reduction by aluminum of a mixture of barium monoxide and
peroxide in an electrically heated vacuum furnace.

The metal is used as a getter in electron tubes to perfect the vacuum
by combining with final traces of gases, as a deoxidizer in copper
refining, and as a constituent in certain alloys. The alloy with nickel
readily emits electrons when heated and is used for this reason in
electron tubes and in spark plug electrodes. The presence of barium
(atomic number 56) after uranium (atomic number 92) had been
bombarded by neutrons was the clue that led to the recognition of
nuclear fission (1939).

Naturally occurring barium is a mixture of seven stable isotopes:
barium-138 (71.66 percent), barium-137 (11.32 percent),
barium-136 (7.81 percent), barium-135 (6.59 percent), barium-134
(2.42 percent), barium-130 (0.101 percent), and barium-132 (0.097
percent). About twice this many radioactive isotopes have been
prepared with mass numbers ranging from 126 to 143. In its
compounds barium has an oxidation state of +2. The Ba2+ ion may
be precipitated from solution by the addition of carbonate (CO32-),
sulfate (SO42-), chromate (CrO42-), or phosphate (PO42-) anions. All
soluble barium compounds are toxic.

Most barium compounds are produced from the sulfate via reduction
to the sulfide. Barium sulfate (BaSO4), a white, heavy powder that
occurs in nature as the mineral barite, is one of the most insoluble
salts known. It is widely used as a filler (e.g., in paper and rubber)
and finds an important application as an opaque medium in the X-ray
examination of the gastrointestinal tract. Lithopone, a mixture of
barium sulfate and zinc sulfide, is a brilliant white pigment.

A number of uses of barium compounds depend on the ready
formation of the highly insoluble sulfate. Thus the compound barium
carbonate (BaCO3), perhaps the most important barium compound,
is employed in removing sulfate from salt brines before they are fed
into electrolytic cells (for the production of chlorine and alkali). The
carbonate also is used to make other barium chemicals, as a flux in
ceramics, and in the manufacture of optical glass, fine glassware, and
ceramic permanent magnets for loudspeakers. Although barium
carbonate is not soluble in water, it dissolves in the hydrochloric acid
of the stomach and thus is used in rat poisons.

Another barium compound, barium chloride (BaCl22H2O),
consisting of colourless crystals that are soluble in water, is utilized in
heat-treating baths, in laboratories as a chemical reagent to precipitate
soluble sulfates, and on a commercial scale with sodium sulfate to
form a white filler and pigment (blanc fixe) for leather, rubber, cloth,
and photographic paper. The oxygen compound barium peroxide
(BaO2) is used for both oxygen production and as a source of
hydrogen peroxide. Volatile barium compounds impart a yellowish
green colour to a flame owing to the emission of light of mostly two
characteristic wavelengths. Barium nitrate, formed with the
nitrogen-oxygen group NO-3, and chlorate, formed with the
chlorine-oxygen group ClO-3, are used for this effect in green signal
flares and fireworks. atomic number 56 atomic weight 137.34 melting
point 725 C boiling point 1,640 C specific gravity 3.5 (20C) valence
2 electronic config. 2-8-18-18-8-2 or (Xe)6s2

"bismuth" Encyclop�dia Britannica Online.

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