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CALCIUM |
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Atomic Number: 20
Atomic Symbol: Ca
Atomic Weight: 40.08
Electron Configuration: -8-8-2
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History
(L. calx, lime) Though lime was prepared by the Romans in the first century under the name calx, the metal was not
discovered until 1808. After learning that Berzelius and Pontin prepared calcium amalgam by electrolyzing lime in
mercury, Davy was able to isolate the impure metal.
Sources
Calcium is a metallic element, fifth in abundance in the earth's
crust, of which if forms more than 3%. It is an essential constituent of leaves, bones, teeth, and shells. Never
found in nature uncombined, it occurs abundantly as limestone, gypsum, and fluorite. Apatite is the fluorophosphate
or chlorophosphate of calcium.
Properties
The metal has a silvery color, is rather hard, and is prepared by electrolysis of the
fused chloride to which calcium fluoride is added to lower the melting point.
Chemically it is one of the alkaline
earth elements; it readily forms a white coating of nitride in air, reacts with water, burns with a yellow-red flame,
forming largely the nitride.
Uses
The metal is used as a reducing agent in preparing other metals such as thorium,
uranium, zirconium, etc., and is used as a deoxidizer, desulfurizer, or decarburizer for various ferrous and
nonferrous alloys. It is also used as an alloying agent for aluminum, beryllium, copper, lead, and magnesium
alloys, and serves as a "getter" for residual gases in vacuum tubes, etc.
Compounds
Its natural and prepared compounds are
widely used. Quicklime (CaO), which is made by heating limestone that is changed into slaked lime by carefully adding water, is the great base of chemical refinery with countless uses.
Mixed with sand it hardens as mortar and
plaster by taking up carbon dioxide from the air. Calcium from limestone is an important element in Portland
cement.
The solubility of the carbonate in water containing carbon dioxide causes the formation of caves with
stalagtites and stalagmites and is responsible for hardness in water. Other important compounds are the carbide,
chloride, cyanamide, hypochlorite, nitrate, and sulfide.
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