Phosphorus (15)

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 colorless 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 vapor 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 vapor pressure of 1 atmosphere at 417°C.

•Name: Phosphorus
•Symbol: P
•Atomic number: 15
•Atomic weight: 30.973762
•Standard state: solid at 298 K
•CAS Registry ID: 7723-14-0
•Group in periodic table: 15
•Group name: Pnictogen
•Period in periodic table: 3
•Block in periodic table: p-block
•Color: colorless/red/silvery white
•Classification: Non-metallic

Historical information

Phosphorus was discovered by Hennig Brand at 1669 in Germany. Origin of name: from the Greek word "phosphoros" meaning "bringer of light" (an ancient name for the planet Venus?). 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.

Physical properties

•Melting point: (white P) 317.3 [or 44.2 °C (111.6 °F)] K
•Boiling point: 550 [or 277 °C (531 °F)] K
•Density of solid: 1823 kg m-3

Orbital properties

•Ground state electron configuration: [Ne].3s2.3p3
•Shell structure: 2.8.5
•Term symbol: 4S3/2
•Pauling electronegativity: 2.19 (Pauling units)

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 usual 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

Interesting Facts:

•When Hennig Brand discovered phosphorus, he became the first person in history to discover an element. (Of course, other elements such as gold and silver were already known – but they had no named discoverer.) The case is similar to the discovery of Uranus by William Herschel in 1781. Other planets had been known for thousands of years, but Herschel was the first person to see and identify Uranus as a new planet.

•Phosphorus compounds are vital for life. Phosphorus is the sixth most abundant element in living organisms. (Now try guessing which elements are more abundant – no search engines allowed until you’ve thought of your own answer!)

•Sir Arthur Conan Doyle's, "The Hound of the Baskervilles," Dr. Watson concluded that the hound had been made to look more terrifying by the ghostly glow of phosphorus, or, since this would most likely have killed the hound, “A cunning preparation of it,” according to Sherlock Holmes.

•White phosphorus ignites spontaneously in air. Red phosphorus needs friction to ignite it, hence its use in matches. Red phosphorus is made by heating white phosphorus to 300°C in the absence of air