Phosphorus: the essentials
Phosphorus is commonly misspelled "phosphorous". It is an essential component of living systems and is found in nervous tissue, bones and cell protoplasm. Phosphorus exists in several allotropic forms including white (or yellow), red, and black (or violet). White phosphorus has two modifications. Ordinary phosphorus is a waxy white solid. When pure, it is colourless and transparent. It is insoluble in water, but soluble in carbon disulphide. It catches fire spontaneously in air, burning to P4O10, often misnamed as phosphorus pentoxide. When exposed to sunlight, or when heated in its own vapour to 250°C, it is converted to the red variety. This form does not ignite spontaneously and it is a little less dangerous than white phosphorus. The red modification is fairly stable and sublimes with a vapour pressure of 1 atmosphere at 417°C.
This sample is from The Elements Collection, an attractive and safely packaged collection of the 92 naturally occurring elements that is available for sale.
Phosphorus: historical information
Phosphorus was discovered in 1669 by Hennig Brand, who prepared it from urine. Not less than 50-60 buckets per experiment in fact, each of which required more than a fortnight to complete.
Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for phosphorus is shown below. [See History of Chemistry, Sir Edward Thorpe, volume 1, Watts & Co, London, 1914.]
Phosphorus around us Read more »
Phosphorus is a key component of biological molecules such as DNA and RNA. Phosphorus is a component of bones, and teeth, and many other compounds required for life. Chronic poisoning of people working unprotected with white phosphorus leads to necrosis of the jaw ("phossy-jaw").
Phosphorus is never found as the free element but is widely distributed in many minerals. Phosphate rock, (apatite, impure calcium phosphate), is an important source of the element. Large deposits are found in Morocco, in Russia, and in the USA.
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Physical properties Read more »
Heat properties Read more »
- Melting point: (white P) 317.3 [44.2 °C (111.6 °F)] K
- Boiling point: 550 [277 °C (531 °F)] K
- Enthalpy of fusion: 0.64 kJ mol-1
Crystal structure Read more »
The solid state structure of phosphorus is: triclinic.
Phosphorus: orbital properties Read more »
Phosphorus atoms have 15 electrons and the shell structure is 2.8.5. The ground state electronic configuration of neutral Phosphorus is [Ne].3s2.3p3 and the term symbol of Phosphorus is 4S3/2.
- Pauling electronegativity: 2.19 (Pauling units)
- First ionisation energy: 1011.8 kJ mol‑1
- Second ionisation energy: 1907 kJ mol‑1
Isolation: originally, phosphorus was extracted from urine. However there is plenty of phosphorus in phosphate ores and those ores represent the usual source for commercially produced phosphorus. There is normally no need to make phosphorus in the laboratory as it is readily available commercially.
The usial route involves heating a phosphate with sand and carbon in an electric furnace. It is highly energy intensive.
2Ca3(PO4)2 + 6SiO2 + 10C (1500°C) → 6CaSiO3 + 10CO + P4
The reaction may proceed via "phosphorus pentoxide", P4O10.
2Ca3(PO4)2 + 6SiO2 + → 6CaSiO3 + P4O10
P4O10 + 10C → 10CO + P4
Phosphorus isotopes Read more »