Calcium
Symbol: Ca
Atomic Number: 20
Atomic Mass: 40.078 amu (atomic mass units)
Melting Point: 839.0 C (1112.15 K, 1542.2 F)
Boiling Point: 1484.0 C (1757.15 K, 2703.2 F)
Number of Protons: 20
Number of Electrons: 20
Number of Neutrons: 20
Classification: Metal
Group Name: Alkaline Earth Metal
Crystal Structure: Cubic
Density @ 293 K: 1.55 grams per cubic centimeter
Color: Silver
The British chemist Sir Humphry Davy discovered the element calcium by using electrolysis on a mixture of lime (CaO) and mercuric oxide (HgO) in 1808. The element gets its name from the Latin word for lime “calx”.
Calcium is a hard, reactive metal. Pure calcium metal when exposed to the atmosphere will develop a white coating of calcium nitride (Ca3N2). The element can be ignited and burns with a yellow/red flame. The metal will also react with water.
Calcium is the fifth most common element to be found in the earth’s crust, making up about 4.2% of the total. Because it can react with water and the gases found in the atmosphere it is never found as a free element. Many different minerals contain calcium including limestone, gypsum and fluorite. The spectacular stalactites and stalagmites to be found in many of the earth’s caves are formed from calcium carbonate (CaCO3).
The element is biologically essential. Calcium phosphate (Ca3(PO4)2) is the main constituent of teeth and bones. Calcium is also found in cell walls and plays an important part in the blood clotting process.
There are six naturally occurring isotopes of calcium four of them are stable while calcium-46 and calcium-48 both have very long half-lives. In order of abundance the naturally occurring isotopes are: calcium-40 (96.94%), calcium-44 (2.09%), calcium-42 (0.647%), calcium-48 (O.187%), calcium-43 (0.135%) and calcium-46 (0.067%). A number of other unstable isotopes of calcium are known with mass numbers ranging from 34 to 56.
Calcium metal has a few industrial uses.
* It is used as a “getter” in vacuum tubes. “Getters” remove trace gases from vacuum tubes.
* Calcium is used to refine zirconium, thorium and uranium.
* Calcium can be used to remove oxygen, sulphur and hydrogen contaminants from alloys.
* A number of metals are alloyed to calcium for different industrial uses. Such alloys include aluminum, copper, lead, beryllium and magnesium.
Many calcium compounds are used within a number of industries. Gypsum or calcium sulfate (CaSO4) is used to make plaster of Paris and in the production of dry wall used by the building industry. Calcium nitrate (Ca(NO3)2) is used as a fertilizer.
The most important of the calcium compounds is calcium carbonate (CaCO3). It forms the rocks limestone, chalk and marble. This compound is the basis of the cement industry. Quick lime (CaO) can be produced from calcium carbonate by heating it. When quick lime is added to water it reacts giving of heat to form slaked lime (Ca(OH)2). Slaked lime has a number of uses in the chemical industry. Other uses for calcium carbonate include the production of white paint, toothpastes, stomach antacids and cleaning powders.
