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Element Fact
Rhenium was the last naturally occurring element to be identified, in 1925. It was so rare that only 1 g of the metal was extracted out of 660 kg of molybdenite ore.

Calcium, Ca

calcium sample

Atomic number: 20
Atomic mass: 40.078(4)
Natural abundance: 46600 ppm
40Ca (39.9625911) - 96.941%
42Ca (41.9586183) - 0.647%
43Ca (42.9587668) - 0.135%
44Ca (43.9554811) - 2.068%
46Ca (45.953693) - 0.004%
48Ca (47.952534) - 0.187%

History and Production

From Latin calx, meaning lime. The latter was already prepared by Romans in the first century for use as a mortar. The metal was first isolated, in impure form, by H. Davy in 1808, after he learnt that J.J. Berzelius and M.M. Pontin produced calcium amalgam by electrolyzing lime in mercury. Nowadays, it is produced by electrolysis of fused calcium chloride (CaCl2). The metal is used as a reducing agent in preparation of other metals such as chromium, zirconium and uranium. It is also used in alloying agent to strength aluminium bearings and also as a scavenger in the steel industry (removes oxygen, sulfur and phosphorus).

Physical Data

calcite mineral It is the fifth most abundant element in earth's crust and third most abundant metal, after aluminium and iron. Mostly exists as sedimentary deposits of calcium carbonate, which represent the fossilized remains of earlier marine life. Calcium also exists in mineral forms such as calcite (left) and aragonite. Both are calcium carbonate (CaCO3) polymorphs minerals. The element is silvery in color. It readily forms a white coating (as shown above) when exposed to air and burns with a yellow-red flame to form mostly the oxide. The solubility of carbonate in water containing carbon dioxide responsible for the formation of stalactites and stalagmites over thousands of years. It is also responsible for the hardening of water.

Interatomic distance: 394.8 pm
Melting point: 842C
Boiling point: 1484C
Thermal conductivity/Wm-1K-1: 200 (27C)
Density/kgm-3: 1550 (20C), 1365 (m.p.)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 177.8 kJ/mol
Gibbs free energy of formation: 144 kJ/mol
Entropy: 154.9 J/mol K
Heat capacity: 20.8 J/mol K

Electronic data

Electronic configuration: [Ar] 4s2
Term symbol: 1S0
Electron affinity: 2.3687 kJ/mol   Electronegativity (Pauline): 1.00
Ionization energy (first, second, third): 589.831, 1145.45, 4912.37 kJ/mol

Chemical properties

Calcium is a very reactive metal. On exposure to air it becomes covered with a whitish coating consisting mainly of calcium hydroxide, Ca(OH)2, and a trace of nitride, Ca3N2. It also react rapidly with water, evolving hydrogen and form the sparingly soluble calcium hydroxide.

Test for calcium
(1) Flame test of calcium salt gives orange-red.
(2) Ammonium carbonate gives a white precipitate of calcium carbonate.
(3) Ammonium ethandioate (oxalate) gives white precipitate of calcium ethandioate. The precipitate can be filtered off, dried and decompose under heat to give calcium oxide. The oxide can be weighed to estimate quantitatively the amount of calcium present in a sample.

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