|
|
Atomic Number: |
20 |
Melting Point: | 842 ºC | |
| Atomic Symbol: | Ca | Boiling Point: | 1484 ºC | ||
| Atomic Weight: | 40.08 amu | Density: | 1550
kg/m 3 |
||
| Atomic Radius: |
197.3 pm |
Oxidation States: | 2 | ||
| Covalent Radius: | 174 pm | Electron Configuration: | [Ar]4s2 | ||
| van der Waals Radius: |
-- |
State of Matter: | solid (paramagnetic) |
(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.
The metal has a silvery color, is rather hard, and is prepared by electrolysis of fused chloride and calcium fluoride ( 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, and burns with a yellow-red flame. Calcium, a metallic element, is fifth in abundance in the earth's crust, of which it 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.
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.
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.
When mixed with sand, it hardens mortar and plaster by taking up carbon dioxide from the air. Calcium from limestone is an important element in Portland cement.
Solubility of the carbonate in water containing carbon dioxide is high, which causes the formation of caves with stalactites and stalagmites and is responsible for hardness in water. Other important compounds are the carbide, chloride, cyanamide, hypochlorite, nitrate, and sulfide.
Calcium has six stable isotopes, two of which occur in nature: stable Ca-40 and radioactive Ca-41 with a half-life of 103,000 years. 97% of the element is in the form of Ca-40. Ca-40 is one of the daughter products of K-40 decay, along with Ar-40. While K-Ar dating has been used extensively in the geological sciences, the prevalence of Ca-40 in nature has impeded its use in dating. Techniques using mass spectrometry and a double spike isotope dilution have been used for K-Ca age dating. Unlike cosmogenic isotopes that are produced in the atmosphere, Ca-41 is produced by neutron activation of Ca-40. Most of its production is in the upper meter or so of the soil column where the cosmogenic neutron flux is still sufficiently strong. Ca-41 has received much attention in stellar studies because Ca-41 decays to K-41, a critical indicator of solar-system anomalies.
Calcium is a rather harmless element and does not have serious hazards.
