Calcium is a chemical element with the symbol Ca and atomic number 20. It is one of the alkaline earth metals in Group 2 (IIa) of the periodic table. It is a reactive metal that forms a dark oxide-nitride film when exposed to air, resembling strontium and barium, its heavier homologues.
Physical and Chemical Properties
With the atomic number 20 and a valence of 2, calcium is trimorphic, harder than sodium but softer than aluminum. It has the second lowest ionization energy in its family of alkali earth metals and is fairly reactive when it is at standard temperature and pressure.
Compounds & Applications
Calcium occurs naturally as limestone (CaCO3), gypsum (CaSO4*2H2O), fluorite and apatite; it is also used in the form of powders for antacids, toothpaste and cleaning powders. It is a vital component of bones and teeth, regulating the levels of other minerals such as phosphorus.
Quicklime, made by heating limestone and changed into slaked lime with the addition of water, is a cheap base for many chemical processes. It is used in the production of white paint, cleaning powders and toothpaste.
Gypsum, a calcium sulphate compound, is commonly used by builders as plaster and nurses for setting bones, i.e. the ‘plaster of Paris’.
Metallic calcium is a reducing agent in some chemical processes to refine thorium, uranium and zirconium. It is also used in some processes to remove oxygen, sulphur and carbon from certain alloys. It is also used in vacuum tubes as a ‘getter’, a material that combines with and removes trace gases from these tubes.