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| A B C D E F G H I J K L M N O P Q R S T U V W X Y Z |
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calcium (Ca)
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Calcium was discovered by Humphry Davy in London in 1808. Its name is derived from the Latin calx, meaning "lime." It is derived by electrolysis of fused calcium chloride and is used as a reducing agent to prepare other metals and in alloys.
Chemistry of calcium
Calcium is generally more reactive than magnesium but not as reactive as sodium or potassium. It reacts quite vigorously with water to form calcium hydroxide and hydrogen. If left exposed to air, it slowly oxidizes to calcium oxide. Calcium react with the halogens to form the corresponding halides. When heated, it reacts with nitrogen to form calcium nitride with sulfur to form calcium sulfide.
All calcium compounds are ionic in nature and are generally less soluble than the corresponding magnesium compounds. Calcium sulfate, carbonate, chromate, and oxalate are all insoluble compounds. Gypsum, used in the manufacture of wallboard, is calcium sulfate dihydrate. Plaster of paris is calcium sulfate hemihydrate. Calcium oxide is called quicklime, and calcium hydroxide is called slaked lime.
| atomic number | 20 |
| relative atomic mass | 40.08 |
| electron configuration | 1s22s22p63s23p64s2 |
| ionization energy | first: 590 kJ/mol second: 1,145 kJ/mol |
| atomic radius | 197 pm |
| ionic radius | 99 pm |
| relative density | 1.55 |
| melting point | 840°C (1,544°F) |
| boiling point | 1,484°C (2,703°F) |
Calcium compounds
Calcium carbonate (CaCO3) is a colorless crystalline solid, occurring naturally as calcite and aragonite, which loses carbon dioxide on heating above 900°C. It is an insoluble base.
Calcium chloride (CaCl2) is a colorless crystalline solid, a by-product of the Solvay process. Being very deliquescent, it is used as an industrial drying agent. Melting point 782°C.
Calcium fluoride (CaF2), or fluorite, is colorless phosphorescent crystalline solid, used as windows in ultraviolet and infrared spectroscopy. Melting point 1,423°C, boiling point c. 2500°C.
Calcium hydroxide (Ca(OH)2), or slaked lime, is a colorless crystalline solid, slightly soluble in water, prepared by hydrating calcium oxide and used in industry and agriculture as an alkali, in mortar, and in glass manufacture.
Calcium oxide (CaO), or quicklime, is white crystalline powder, made by calcination of calcium carbonate minerals, which reacts violently with water to give calcium hydroxide and is used in arc lights and as an industrial dehydrating agent. Melting point 2,580°C, boiling point 2,850°C.
Calcium sulfate (CaSO4) is a colorless crystalline solid, occurring naturally as gypsum and anhydrite. When the dihydrate is heated to 128°C, it loses water, forming the hemihydrate, plaster of paris. This re-forms the dihydrate as a hard mass when mixed with water, and is used for casts.
Calcium and life
Calcium is essential to terrestrial vertebrate life, being the basic constituent of bones and teeth (calcium phosphate) and playing an important role in many metabolic processes, including nerve function, muscle contraction, and blood clotting (see also elements, biological abundance). It is the most abundant mineral in the body; an average-sized person carries about 0.9 to 1.1 kg of calcium, mostly in the bones. Calcium, in the form of calcium carbonate, also occurs in the shells of invertebrates.
The main dietary sources of calcium are dairy products, eggs, and green, leafy vegetables. Calcium may also be added to flour.
Related category
• INORGANIC CHEMISTRY
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