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For cement and plaster of paris.
| Atomic Number: |
20 |
| Atomic Symbol: |
Ca |
| Atomic Weight: |
40.08 |
| Electron Configuration: |
[Ar]4s2 |
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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