CaO(s) + CO2(g)
Calcium is a metal in Group IIA - the alkaline earth metals - in the 4th period. Other elements in this group are beryllium (Be), magnesium (Mg), strontium (Sr), barium (Ba), and radium (Ra).
The Romans prepared lime in the first century by heating limestone, and it was considered an element until the late eighteenth century. However, Lavoisier believed lime to be an oxide of an as-yet unisolated metallic substance. In 1808, after learning that Berzelius and Pontin had prepared calcium amalgam by electrolyzing lime in mercury, Davy was able to isolate the impure metal.
The name is derived from the Latin word, calx, for lime. The symbol Ca is an abbreviation of the name.
Ca is the fifth most abundant element in the earth's crust, but is never found uncombined. The order of abundance of the first six elements is:
The silvery, rather hard metal is prepared by electrolysis of fused calcium chloride to which CaF2 is added to lower the melting point.
Calcium metal is an active element; it tarnishes rapidly when exposed to air and burns with a bright flame when heated to give the oxide (CaO) and nitride (Ca3N2).
Chemically calcium is one of the alkaline earth elements. It readily forms a white coating of nitride (Ca3N2) and oxide (CaO) in air, reacts with water to give the hydroxide, burns brightly when heated in air to form largely the nitride. It combines with several elements, e.g., with oxygen, carbon, hydrogen, chlorine, fluorine, arsenic, phosphorus, and sulfur, forming numerous compounds.
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" to remove residual gases from vacuum tubes.
Although calcium metal is of only minor commercial importance, calcium compounds are widely and diversely used. Calcium is an essential constituent of leaves, bones, teeth and shells. Never found in nature uncombined, it occurs abundantly as limestone, coral, and marble, all calcium carbonate. (Two forms of CaCO3 are calcite and aragonite.) Other important minerals are gypsum (calcium sulfate), fluorite (calcium fluoride), and apatite. Apatite is the fluorophosphate or chlorophosphate of calcium.
Quicklime (calcium oxide) is made by heating limestone
CaCO3(s) + heat CaO(s) + CO2(g)
and changed into slaked lime by the careful addition of water.
CaO(s) + H2O(liq)
Ca(OH)2(s) + heat
It is widely used as an inexpensive base in the chemical industry. Mixed with sand, quicklime hardens as mortar by taking up carbon dioxide from the air. Calcium from limestone is an important element in Portland cement. The solubility of calcium carbonate in water containing dissolved carbon dioxide causes the formation of caves with stalactites and stalagmites. Calcium salts are also major contributors to hardness in water.