Phosphorus

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Phosphorus

This is phosphorus.

Symbol P
Atomic number 15
Atomic mass 30.9738 amu

Phosphorus, discovered in 1669, is a nonmetal. The most common form of phosphorus, as well as some of its compounds, are noted for their ability to glow in the dark.

Distinguishing properties

Phosphorus is an essential constituent of the living tissue and bones. It plays a very important part in metabolic processes (as adenosine triphosphate), muscle action and hardening on bones and teeth (as hydroxyapatite).

Forms

Phosphorus exists in three common allotropes:

  1. White phosphorus is a white, waxy substance. It is soft, very reactive and consists of P4 molecules. It is so unstable that it turns yellow (as shown above) then reddens in light, and glows in the dark - hence "phosphorescence". It is the most volatile and explosive of the three basic allotropic forms. Hence white phosphorus is kept under water to isolate it from the air. This allotropic form of phosphorus is also the most useful in the production of other compounds of phosphorus.
  2. Red phosphorus, as shown above, is formed by exposing white phosphorus to sunlight or heating it under pressure to above 275°C. This form is fairly stable, but the heat from simple friction is enough to convert it to explosive white phosphorus. This feature is used to great advantage in the manufacture of safety matches.
  3. Black phosphorus is also produced by heating white phosphorus in the presence of a mercury catalyst and a seed crystal of black phosphorus. Black phosphorus is the least reactive, does not ignite easily and has the least commercial value.

Usage

Phosphorus produced today are used in:

  • fireworks and pyrotechnic devices.
  • fertilizers. Phosphorus is essential for plant growth and phosphorus compoudns are constituents in many fertilizers. The most common common is superphosphate.
  • safety matches.
  • organophosphorus pesticides, which contains P4S10.
  • gaskets and O-rings in spacecrafts. These use polyphosphazenes, which have properties similar to silicones. Materials made out of polyphosphazenes are water repellent, flame and solvent resistant, and flexible at low temperature.
  • food industry. H3PO4, phosphoric acid, is an ingredient in Coca-Cola. An aqueous solution of this acid has a tangy taste.
  • detergents industry.
  • flame retardants. Phosphorus compounds such as tricresyl phosphate, phosphorus oxychloride, and phosphoric anhydride are substances that reduces the combustibility of a material.

Common compounds

Phosphorus is wide-spread throughout the world in rock structures such as phosphate rock (Ca3(PO4)2) and the apatites. Guano deposits found on islands frequented by sea birds are also an important source of phosphorus. The element is obtained industrially by the heating phosphate rock in sand (SiO2) and coke (carbon) in an electric furnace of 1450°C. The phosphorus produced is P4 and collected under water as white phosphorus.

See also

Periodic table of the elements