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    calcium (Ca)

    calcium
    A soft, gray, metallic element that tarnishes rapidly on exposure to air. Calcium is one of the alkaline earth metals. It occurs commonly on Earth (see elements, terrestrial abundance), in various forms of its carbonate (CaCO3), e.g., chalk, limestone, and marble, and its sulfate (CaSO4), e.g. gypsum. Its compounds are used to make plaster, quicklime, Portland cement, and metallurgic and electronic materials.

    Calcium was discovered by Humphry Davy in London in 1808. Its name is derived from the Latin calx, meaning "lime".


    Chemistry of carbon

    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 anufacture 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 and life

    Calcium is essential to terrestrial vertebrate life, being the basic constituent of bones and teeth 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 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


    External site
    calcium (interactive periodic table)



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