Discovered in 1669, phosphorus exists in three common allotropes:
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.
Red phosphorus, as shown above, is formed by exposing white phosphorus
to sunlight or heating it under pressure to above 275oC. 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.
Black phosphorus is also produced by heating white phosphorus in
the presence of a mercurycatalyst
and a seed crystal of black phosphorus. Black phosphorus is the least reactive,
does not ignite easily and has the least commercial value.
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 1450oC. The phosphorus produced is P4 and collected
under water as white phosphorus.
Phosphorus 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. 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.
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.
flame retardants. Phosphorus compounds such as tricresyl phosphate, phosphorus
oxychloride, and phosphoric anhydride are substances that reduces the combustibility
of a material.
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).