Phosphorus

Phosphorus

Phosphorus is a chemical element with symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidised state, as inorganic phosphate rocks. Elemental phosphorus exists in two major forms—white phosphorus and red phosphorus—but due to its high reactivity, phosphorus is never found as a free element on Earth.

The first form of elemental phosphorus to be produced (white phosphorus, in 1669) emits a faint glow upon exposure to oxygen – hence its name given from Greek mythology, meaning "light-bearer" (Latin Lucifer), referring to the "Morning Star", the planet Venus. The term "phosphorescence", meaning glow after illumination, originally derives from this property of phosphorus, although this word has since been used for a different physical process that produces a glow. The glow of phosphorus itself originates from oxidation of the white (but not red) phosphorus— a process now termed chemiluminescence.

The vast majority of phosphorus compounds are consumed as fertilisers. Other applications include the role of organophosphorus compounds in detergents, pesticides and nerve agents, and matches.

Phosphorus is essential for life. As phosphate, it is a component of DNA, RNA, ATP, and also the phospholipids that form all cell membranes. Demonstrating the link between phosphorus and life, elemental phosphorus was historically first isolated from human urine, and bone ash was an important early phosphate source. Phosphate minerals are fossils. Low phosphate levels are an important limit to growth in some aquatic systems. The chief commercial use of phosphorus compounds for production of fertilisers is due to the need to replace the phosphorus that plants remove from the soil.

Occurrence


In terms of stellar nucleosynthesis, stable forms of phosphorus are produced in large (greater than 3 solar masses) stars by fusing two oxygen atoms together.[citation needed] This requires temperatures above 1,000 megakelvins.

Phosphorus is not found free in nature, but it is widely distributed in many minerals, mainly phosphates. Historically-important but limited commercial sources were organic, such as bone ash and (in the latter 19th century) guano. Inorganic phosphate rock, which is partially made of apatite (an impure tri-calcium phosphate mineral), is today the chief commercial source of this element. About 50 percent of the global phosphorus reserves are in the Arab nations. Large deposits of apatite are located in China, Russia, Morocco, Florida, Idaho, Tennessee, Utah, and elsewhere. Albright and Wilson in the United Kingdom and their Niagara Falls plant, for instance, were using phosphate rock in the 1890s and 1900s from Tennessee, Florida, and the Îles du Connétable (guano island sources of phosphate); by 1950 they were using phosphate rock mainly from Tennessee and North Africa. In the early 1990s Albright and Wilson's purified wet phosphoric acid business was being adversely affected by phosphate rock sales by China and the entry of their long-standing Moroccan phosphate suppliers into the purified wet phosphoric acid business.

In 2012, the USGS estimated 71 billion tons of world reserves, where reserve figures refer to the amount assumed recoverable at current market prices; 0.19 billion tons were mined in 2011.

Recent reports suggest that production of phosphorus may have peaked, leading to the possibility of global shortages by 2040. In 2007, at the rate of consumption, the supply of phosphorus was estimated to run out in 345 years. However, some scientists now believe that a "peak phosphorus" will occur in 30 years and that "At current rates, reserves will be depleted in the next 50 to 100 years." Phosphorus comprises about 0.1% by mass of the average rock, and consequently the Earth's supply is vast, although dilute.

Symbol		P
Atomic Number		15
Atomic Weight		30.973762
Oxidation States		+3, +5, -3
Electronegativity, Pauling		2.19
State at RT		Solid, Nonmetal
Melting Point, K		317.3
Boiling Point, K		553

Interesting Facts about Phosphorus

• 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!)
• In 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 oC in the absence of air.

Appearance and Characteristics

Harmful effects:

White phosphorus is highly toxic. Skin contact can result in severe burns. Red phosphorus (provided it is not contaminated with white phosphorus) is considered non-toxic.

Characteristics:

• White phosphorus is a highly reactive, waxy, white-yellow, transparent solid with acrid fumes. It emits a weak green glow (luminescence) in the presence of oxygen. It is insoluble in water, but soluble in carbon disulfide. White phosphorus ignites spontaneously in air, burning to the pentoxide (P4O10).
• Phosphorus exists in two other main allotropic forms: red, and black (or violet).
• Red phosphorus results when white phosphorus is heated or exposed to sunlight.
• Black phosphorus is the least reactive allotrope and has a graphite-like structure.

Uses of Phosphorus

• Phosphorus is a vital plant nutrient and its main use – via phosphate compounds – is in the production of fertilizers. Just as there are biological carbon and nitrogen cycles, there is also a phosphorus cycle.
• Phosphorus is used in the manufacture of safety matches (red phosphorus), pyrotechnics and incendiary shells.
• Phosphorus is also used in steel manufacture and in the production of phosphor bronze.
• Phosphates are ingredients of some detergents.
• Phosphorus is used to make light-emitting diodes (LEDs).