Calcium is the chemical element with atomic number 20,
symbol Ca.
It is a fairly hard gray-white alkaline earth metal. There is no such thing as a
pure body in nature. It is the fifth most abundant element of the earth's crust
(more than 3%). It is vital for many species: formation of bones, teeth and
shells (it makes up 1 to 2% of the weight of the human body of an adult9).
Calcium also plays a very important role in cell physiology, while being a
cellular poison beyond a certain dose.
Calcium has 24 known isotopes with a mass number between 34 and 57, but no known
nuclear isomer. Five of these isotopes are stable, 40Ca, 42Ca, 43Ca, 44Ca and
46Ca (but 40Ca and 46Ca are suspected of being extremely long-lived
radioisotopes, but no decay has yet been observed), and one radioisotope (48Ca)
has such a long half-life (43 กม 1018 years, almost 3 billion times the age of
the universe) that it is considered for practical cases as stable. Calcium 40
represents 97% of natural calcium.
Notable features
Calcium can be produced by electrolysis of calcium fluoride but more commonly by
vacuum reduction of lime (CaO) with aluminum powder.
It burns with a yellow-red flame; exposed to dry air it forms a white protective
layer of oxide and nitride. It reacts violently with the water from which it
displaces the hydrogen and then forms calcium hydroxide Ca (OH) 2.
Physical applications of calcium metal
reducing agent in the extraction of other metals such as uranium, zirconium, and
thorium;
deoxidizer, desulfurizer or decarburizer for different ferrous and non-ferrous
alloys;
used, sometimes in combination with magnesium, to remove bismuth from lead (debismuthage);
alloying agent used in the production of aluminum, beryllium, copper, lead and
magnesium alloys.
Compounds
In all of its known compounds, calcium is present in the form of the Ca2 +
cation.
Calcium aluminate Ca3 (AlO3) 2 or (Al2O3, 3 CaO): one of the components of
clinker, and used for the manufacture of refractory mortars;
Calcium carbonate CaCO3, very widespread in nature, because it is the basic
component of limestone rocks; quicklime is obtained by calcining the limestone;
see also: calcite, aragonite;
Calcium carbide CaC2 (commonly known as carbide; its hydrolysis produces
acetylene);
Halides:
Calcium chloride CaCl2 sometimes used as a snow-removing salt to replace sodium
chloride;
Calcium fluoride CaF2 (fluorite);
Calcium iodide CaI2;
Calcium bromide CaBr2;
Calcium hypochlorite Ca (ClO) 2;
Calcium nitrate Ca (NO3) 2;
Calcium nitride Ca3N2;
Oxides and hydroxide:
Calcium oxide CaO (quicklime),
Calcium hydroxide Ca (OH) 2 (slaked lime),
Calcium peroxide CaO2;
Phosphates:
Calcium phosphate Ca3 (PO4) 2,
Hydroxyapatite Ca10 (PO4) 6 (OH) 2 Component of teeth and bones;
Calcium phosphide Ca3P2 (its hydrolysis produces phosphine PH3);
Sulfates:
Anhydrous calcium sulfate anhydrous CaSO4, dehydrating,
Bassanite calcium sulphate semi-hydrated 2 (CaSO4) .H2O principal constituting
plaster powder before use,
Hydrated calcium sulphate gypsum CaSO4.2H2O, main constituent of plaster after
hardening;
Calcium sulfide CaS.
Calcium can also combine with various other metals. The calcium-silicon alloy,
called silico-calcium, is an adjuvant in the preparation of certain steels.
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rhenium germanium zirconium cadmium hafnium
barium lithium beryllium strontium calcium
Tantalum gadolinium samarium yttrium ytterbium
Lutetium praseodymium holmium erbium thulium dysprosium
terbium europium lanthanum cerium neodymium scandium
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