Phosphorus
Symbol: P
Atomic Number: 15
Atomic Mass: 30.97376 amu (atomic mass units)
Melting Point: 44.1 C (317.25 K, 111.38 F)
Boiling Point: 280.0 C (553.15 K, 536.0 F)
Number of Protons: 15
Number of Electrons: 15
Number of Neutrons: 16
Classification: Non-metal
Group Name: Pnictogen
Crystal Structure: Monoclinic
Density @ 293 K: 1.82 grams per cubic centimeter
Color: white
In 1699 the German physician and alchemist Hennig Brand showed remarkable tenacity in his discovery of the element phosphorus. To extract the element he processed 60 buckets of human urine. Part of his extraction method involved boiling and filtering the urine. The name phosphorus comes from the Greek for light bearing “phosphoros”.
To the relief of those working in the chemical extraction industry today phosphorus has been found in a number of rocks and can be extracted from phosphate rock that contains the mineral apatite (Ca3(PO4)2). It is extracted by heating the phosphate rock in a furnace with carbon and sand (silica).
There are three main allotropes of phosphorus each with different properties. These allotropes are white, red and black phosphorus.
The most common allotrope is white phosphorus. White phosphorus with ignite spontaneously in air and burns to form the pentoxide (P4O10). For this reason it is stored under water. It has two modifications alpha and beta; the transmission temperature for these modifications is minus 3.8 C (235 K, 25.16 F). Ordinary phosphorus is a white waxy solid. When in the pure state white phosphorus is transparent and colorless. White phosphorus is poisonous 50 milligrams is considered a lethal dose. Chronic poisoning with white phosphorus can lead to necrosis of the jaw this is commonly known as “phossy jaw”.
White phosphorous is used to make many different compounds. It is also used by the military to make incendiary and smoke bombs. In the metal making industry it is used in the production of some types of steel and phosphor bronze.
The phosphorus compounds which are commercially valuable are:
* Phosphoric acid (H3PO4) – used in soft drinks and to make other phosphate compounds.
* Triple super phosphate (Ca(H2PO4)2H2O) – used as a fertilizer.
* Calcium phosphate (Ca3(PO4)2) – used to make baking powder and in china production.
* Trisodium phosphate (Na3PO4) – used as a water softener and a cleaning agent.
* Other phosphorus compounds exhibit phosphorescence and will glow in the dark or emit light when exposed to radiation. These compounds are used in fluorescent light tubes and television tubes.
White phosphorus can be transformed into red phosphorus by exposure to sunlight or by heating to 250 C (523 K, 482 F). Red phosphorus is not as reactive as white phosphorus nor is it poisonous. The red phosphorus allotrope can revert back to the white form with frictional rubbing. Red phosphorous sublimes from a solid to a gas at a vapor pressure of one atmosphere and a temperature of 417 C (690 K, 483F).
Red phosphorus is used in the manufacture of safety matches, fireworks and some pesticides.
Black phosphorus is formed from white phosphorus by heating with a mercury catalyst and a seed crystal of black phosphorus. This allotrope is the least reactive form of phosphorus. Black phosphorous has very few commercial applications.
Phosphorus has one naturally occurring isotope that is phosphorus-31 and it is stable. Unstable isotopes with mass numbers which range from24 to 46 are known.
Phosphorus is biologically essential. It is found in cell cytoplasm and cell walls and it is a component of both DNA and RNA. Phosphorus is also found in teeth and bones.
