calcium (kăl`sēəm) [Lat.,=lime], metallic chemical element; symbol Ca; at. no. 20; at. wt. 40.08; m.p. about 839°C;; b.p. 1,484°C;; sp. gr. 1.55 at 20°C;; valence +2. Calcium is a malleable, ductile, silver-white, relatively soft metal with face-centered, cubic crystalline structure. Chemically it resembles strontium and barium; it is classed with them as an alkaline-earth metal alkaline-earth metals, metals constituting Group 2 of the periodic table . Generally, they are softer than most other metals, react readily with water (especially when heated), and are powerful reducing agents, but they are exceeded in each of these properties by the
..... Click the link for more information. in Group 2 of the periodic table periodic table, chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley . In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the
..... Click the link for more information. . Calcium is chemically active; it tarnishes rapidly when exposed to air and burns with a bright yellow-red flame when heated, mainly forming the nitride. It reacts directly with water, forming the hydroxide. It combines with other elements, e.g., with oxygen, carbon, hydrogen, chlorine, fluorine, arsenic, phosphorus, and sulfur, forming many compounds.

Although lime (calcium oxide) has been known since ancient times, elemental calcium was first isolated by Sir Humphry Davy in 1808. Today, calcium metal is usually prepared by electrolysis of fused calcium chloride to which a little calcium fluoride has been added. It is used in alloys with other metals, such as aluminum, lead, or copper; in preparation of other metals, such as thorium and uranium, by reduction; and (like barium) in the manufacture of vacuum tubes to remove residual gases.

The metal is of little commercial importance compared to its compounds, which are widely and diversely used. The element is a constituent of lime (see calcium oxide calcium oxide, chemical compound, CaO, a colorless, cubic crystalline or white amorphous substance. It is also called lime, quicklime, or caustic lime, but commercial lime often contains impurities, e.g., silica, iron, alumina, and magnesia.
..... Click the link for more information. ), chloride of lime (bleaching powder), mortar mortar, in building, mixture of lime or cement with sand and water, used as a bedding and adhesive between adjacent pieces of stone, brick, or other material in masonry construction.
..... Click the link for more information. , plaster, cement (see cement cement, binding material used in construction and engineering, often called hydraulic cement, typically made by heating a mixture of limestone and clay until it almost fuses and then grinding it to a fine powder.
..... Click the link for more information. , concrete concrete, structural masonry material made by mixing broken stone or gravel with sand, cement , and water and allowing the mixture to harden into a solid mass.
..... Click the link for more information. , whiting whiting, white, powdery substance, prepared by grinding chalk or some other source of calcium carbonate. When mixed with linseed oil it forms putty , and with water and several other substances it constitutes whitewash .
..... Click the link for more information. , putty, precipitated chalk chalk, mineral of calcium carbonate , similar in composition to limestone, but softer. It is characteristically a marine formation and sometimes occurs in great thickness; the chief constituents of these chalk deposits are the shells of minute animals called
..... Click the link for more information. , gypsum gypsum (jĭp`səm), mineral composed of calcium sulfate (calcium, sulfur, and oxygen) with two molecules of water, CaSO₄
..... Click the link for more information. , and plaster of Paris. Tremolite, a form of asbestos asbestos, common name for any of a variety of silicate minerals within the amphibole and serpentine groups that are fibrous in structure and more or less resistant to acid and fire. Chrysotile asbestos, a form of serpentine , is the chief commercial asbestos.
..... Click the link for more information. , is a naturally occurring compound of calcium, magnesium, silicon, and oxygen. Calcium carbide reacts with water to form acetylene gas; it is also used to prepare calcium cyanamide, which is used as a fertilizer. The phosphate is a major constituent of bone ash. The arsenate and the cyanide are used as insecticides. Calcium bicarbonate causes temporary hardness in water; calcium sulfate causes permanent hardness. Generally, calcium compounds show an orange or yellow-red color when held in the Bunsen burner flame.

Although calcium is the fifth most abundant element in the earth's crust, of which it constitutes about 3.6%, it is not found uncombined. It is found widely distributed in its compounds, e.g., Iceland spar Iceland spar, colorless variety of crystallized calcite , characterized by its properties of transparency and double refraction. It is used chiefly in the manufacture of Nicol prisms , which are essential parts of polarizing microscopes and other optical instruments.
..... Click the link for more information. , marble marble, metamorphic rock composed wholly or in large part of calcite or dolomite crystals, the crystalline texture being the result of metamorphism of limestone by heat and pressure.
..... Click the link for more information. , limestone limestone, sedimentary rock wholly or in large part composed of calcium carbonate. It is ordinarily white but may be colored by impurities, iron oxide making it brown, yellow, or red and carbon making it blue, black, or gray. The texture varies from coarse to fine.
..... Click the link for more information. , feldspar feldspar (fĕl`spär, fĕld`–) or felspar
..... Click the link for more information. , apatite apatite (ăp`ətīt)
..... Click the link for more information. , calcite calcite (kăl`sīt), very widely distributed mineral, commonly white or colorless, but appearing in a great variety of colors owing to
..... Click the link for more information. , dolomite 1 Mineral, calcium magnesium carbonate, CaMg (CO₃)₂. It is commonly crystalline and is white, gray, brown, or reddish in color with a vitreous to pearly luster. The magnesium is sometimes replaced in part by iron or manganese.
..... Click the link for more information. , fluorite fluorite (fl
..... Click the link for more information. , garnet garnet, name applied to a group of isomorphic minerals crystallizing in the cubic system. They are used chiefly as gems and as abrasives (as in garnet paper).
..... Click the link for more information. , and labradorite labradorite (lăb`rədôrīt', lăbrədôr`īt), a variety of plagioclase feldspar .
..... Click the link for more information. . It is a constituent of most plant and animal matter.

Calcium is essential to the formation and maintenance of strong bones and teeth. In the human adult the bone calcium is chiefly in the form of the phosphate and carbonate salts. A sufficient store of vitamin D in the body is necessary for the proper utilization of calcium. Calcium also functions in the regulation of the heartbeat and in the conversion of prothrombin to thrombin, a necessary step in the clotting of blood.

calcium

Chemical element, one of the alkaline earth metals, chemical symbol Ca, atomic number 20. The most abundant metallic element in the human body, it is an essential part of bones and teeth and has many physiological functions (see calcium deficiency; tooth). It is the fifth most abundant element in Earth's crust but does not occur naturally in the free state. In its compounds calcium has valence 2. It occurs in limestone, chalk, marble, dolomite, eggshells, pearls, coral, and many marine shells as calcium carbonate, or calcite; in apatite as calcium phosphate; in gypsum as calcium sulfate; and in many other minerals. It is used as an alloying agent and in other metallurgical applications; its alloy with lead is used in cable sheathing and grids for batteries. Calcite is used as a lime source, a filler, a neutralizer, and an extender; in pure form it is used in baking powder and as an antacid and calcium supplement. Calcium oxide (lime) and its product after water addition, calcium hydroxide (slaked lime), are important industrially. Other significant compounds are calcium chloride (a drying agent), calcium hypochlorite (a bleach), calcium sulfate (gypsum and plaster of paris), and calcium phosphate (a plant food and stabilizer for plastics).

calcium (redirected from calcium borogluconate)

calcium

calcium
(redirected from calcium borogluconate)