Phosphorus is a nonmetal in the 3rd period of Group VA. Other members of the group are nitrogen (N), arsenic (As), antimony (Sb), and bismuth (Bi).
Phosphorus was discovered in 1669 by Hennig Brand, an alchemist, who prepared it from urine. This preparation of phosphorous was a carefully guarded secret and was the only source known until about 1770, when it was obtained from bones by Gahn and Scheele.
The name is derived from the Greek word, phosphoros, meaning light-bearing. The symbol P is an abbreviation of the name.
Phosphorus exists in three allotropic forms: white (or yellow), red, and black (or violet).
Never found free in nature, it is widely distributed in combination with minerals. Phosphate rock, which contains the mineral apatite, an impure tricalcium phosphate, Ca3(PO4)2, is an important source of the element. Large deposits are found in the U.S.S.R., in Morocco, and in Florida, Tennessee, Utah, and Idaho.
Ordinary phosphorus is a waxy white solid. When pure it is colorless and transparent. It is insoluble in water, but soluble in carbon disulfide. It takes fire spontaneously in air, burning to give P4O10.
P4(s) + 5 O2(g) P4O10(s)
For this reason, white phosphorus should be kept under water, and it should be handled with forceps, as contact with the skin may cause severe burns. In addition, it is very poisonous.
White phosphorus may be made by several methods. In one process, tricalcium phosphate, the essential ingredient of phosphate rock, is heated in the presence of carbon and silica in an electric furnace or fuel-fired blast furnace. Elementary phosphorus is liberated as vapor and may be collected under water.
2 Ca3(PO4)2(s) + 10 C(s) + 6 SiO2(s)
6 CaSiO3(s) + 10 CO(g) + P4(s)
If desired, the phosphorus vapor and carbon monoxide produced by the reaction can be oxidized at once in the presence of moisture or water to produce phosphoric acid, an important compound in making super-phosphate fertilizers.
When exposed to sunlight or when heated in its own vapor to 250°C, white phosphorus is converted to the red variety, which does not phosphoresce in air like the white variety. The red form does not ignite spontaneously, and it is not as dangerous as white phosphorus. It should, however, be handled with care as it does convert to the white form at some temperatures, and it emits highly toxic fumes of the oxides of phosphorus when heated. The red modification is fairly stable, sublimes with a vapor pressure of 1 atm. at 417°C, and is used in the manufacture of safety matches, pyrotechnics, pesticides, incendiary shells, smoke bombs, tracer bullets, etc.
Phosphorus compounds are widely used for many purposes. World-wide demand for fertilizers has led to record phosphate production in recent years. Phosphates are used in the production of special glasses, such as those used for sodium lamps. Bone-ash, calcium phosphate, is also used to produce fine chinaware and to give mono-calcium phosphate, CaHPO4, which is used in baking powder. Phosphorus is also important in the production of steels, phosphor bronze, and many other products. Sodium phosphates are important as cleaning agents, as water softeners, and for preventing boiler scale and corrosion of pipes and boiler tubes.
Phosphorus, as phosphate, is an essential ingredient of all cell protoplasm, nervous tissue, and bones. It is also present in plants and animals, and is a constituent of the fundamental energy source, adenosine triphosphate. Compounds containing phosphorus are essential in the food of living things.