Phosphorus

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15 siliconphosphorussulfur
N

P

As
General
Name, symbol, number phosphorus, P, 15
Chemical series nonmetals
Group, period, block 153, p
Appearance waxy white/ red/
black/ colorless
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Standard atomic weight 30.973762(2)g·mol−1
Electron configuration [Ne] 3s2 3p3
Electrons per shell 2, 8, 5
Density (near r.t.) (white) 1.823 g·cm−3
Density (near r.t.) (red) 2.34 g·cm−3
Density (near r.t.) (black) 2.69 g·cm−3
Melting point (white) 317.3 K
(44.2 °C, 111.6 °F)
Boiling point 550 K
(277 °C, 531 °F)
Heat of fusion (white) 0.66 kJ·mol−1
Heat of vaporization 12.4 kJ·mol−1
Heat capacity (25 °C) (white)
23.824 J·mol−1·K−1
Vapor pressure (white)
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 279 307 342 388 453 549
Vapor pressure (red)
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 455 489 529 576 635 704
Oxidation states 5, 4, 3, 2 [1], 1 [2], -3
(mildly acidic oxide)
Electronegativity 2.19 (Pauling scale)
Ionization energies
(more)
1st: 1011.8 kJ·mol−1
2nd: 1907 kJ·mol−1
3rd: 2914.1 kJ·mol−1
Atomic radius 100 pm
Atomic radius (calc.) 98 pm
Covalent radius 106 pm
Van der Waals radius 180 pm
Miscellaneous
Magnetic ordering no data
Thermal conductivity (300 K) (white)
0.236 W·m−1·K−1
Bulk modulus 11 GPa
CAS registry number 7723-14-0
Selected isotopes
Main article: Isotopes of phosphorus
iso NA half-life DM DE (MeV) DP
31P 100% 31P is stable with 16 neutrons
32P syn 14.28 d β- 1.709 32S
33P syn 25.3 d β- 0.249 33S
References
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Phosphorus, (IPA: /ˈfɒsfərəs/), is the chemical element that has the symbol P and atomic number 15. The name comes from the Greek: phôs (meaning "light") and phoros (meaning "bearer"). A multivalent nonmetal of the nitrogen group, phosphorus is commonly found in inorganic phosphate rocks.

Due to its high reactivity, phosphorus is never found as a free element in nature on Earth. One form of phosphorus (white phosphorus) emits a faint glow upon exposure to oxygen (hence its Greek derivation and the Latin 'light-bearer', meaning the planet Venus as Hesperus or "Morning Star").

Phosphorus is a component of DNA and RNA and an essential element for all living cells. The most important commercial use of phosphorus-based chemicals is the production of fertilizers.

Phosphorus compounds are also widely used in explosives, nerve agents, friction matches, fireworks, pesticides, toothpaste, and detergents.

Contents

[edit] Characteristics

[edit] Allotropes

Phosphorus is an excellent example of an element that exhibits allotropy, as its various allotropes have strikingly different properties.

The two most common allotropes are white phosphorus and red phosphorus. A third form, scarlet phosphorus, is obtained by allowing a solution of white phosphorus in carbon disulphide to evaporate in sunlight. A fourth allotrope, black phosphorus, is obtained by heating white phosphorus under very high pressures (12,000 atmospheres) In appearance, properties and structure it is very like graphite, being black and flaky, a conductor of electricity and has puckered sheets of linked atoms. Another allotrope is diphosphorus - which is highly reactive.

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White phosphorus (P4) exists as individual molecules made up of four atoms in a tetrahedral arrangement, resulting in very high ring strain and instability. It contains 6 single bonds.

White phosphorus is a white, waxy transparent solid. This allotrope is thermodynamically unstable at normal condition and will gradually change to red phosphorus. This transformation, which is accelerated by light and heat, makes white phosphorus almost always contain some red phosphorus and appear yellow. For this reason, it is also called yellow phosphorus. It glows greenish in the dark (when exposed to oxygen), is highly flammable and pyrophoric (self-igniting) upon contact with air as well as toxic (causing severe liver damage on ingestion). The odour of combustion of this form has a characteristic garlic smell, and samples are commonly coated with white "(di)phosphorus pentoxide", which consists of P4O10 tetrahedra with oxygen inserted between the phosphorus atoms and at their vertices. White phosphorus is insoluble in water but soluble in carbon disulfide.

The white allotrope can be produced using several different methods. In one process, calcium phosphate, which is derived from phosphate rock, is heated in an electric or fuel-fired furnace in the presence of carbon and silica[1]. Elemental phosphorus is then liberated as a vapour and can be collected under phosphoric acid. This process is similar to the first synthesis of phosphorus from calcium phosphate in urine.

Red phosphorus may be formed by heating white phosphorus to 250°C (482°F) or by exposing white phosphorus to sunlight. Phosphorus after this treatment exists as an amorphous network of atoms which reduces strain and gives greater stability; further heating results in the red phosphorus becoming crystalline. Red phosphorus does not catch fire in air at temperatures below 240°C, whereas white phosphorus ignites at about 30°C.

In 1865 Hittorf discovered that when phosphorus was recrystallized from molten lead, a red/purple form is obtained. This purple form is sometimes known as "Hittorf's phosphorus." In addition, a fibrous form exists with similar phosphorus cages. Below is shown a chain of phosphorus atoms which exhibits both the purple and fibrous forms.

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One of the forms of red/black phosphorus is a cubic solid.[2]

Black phosphorus has an orthorhombic structure (Cmca) and is the least reactive allotrope, it consists of many six-membered rings which are interlinked. Each atom is bonded to three other atoms.[3][4] A recent synthesis of black phosphorus using metal salts as catalysts has been reported.[5]

The diphosphorus allotrope (P2) can be obtained normally only under extreme conditions (for example, from P4 at 1100 kelvin). Nevertheless, some advancements were obtained in generating the diatomic molecule in homogeneous solution, under normal conditions with the use by some transitional metal complexes (based on for example tungsten and niobium).[6]

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[edit] Glow

The glow from phosphorus was the attraction of its discovery around 1669, but the mechanism for that glow was not fully described until 1974.[7] It was known from early times that the glow would persist for a time in a stoppered jar but then cease. Robert Boyle in the 1680s ascribed it to "debilitation" of the air; in fact it is oxygen being consumed. By the 18th century it was known that in pure oxygen phosphorus does not glow at all,[8] there is only a range of partial pressure where it does. Heat can be applied to drive the reaction at higher pressures.[9]

In 1974 the glow was explained by R. J. van Zee and A. U. Khan.[7] A reaction with oxygen takes place at the surface of the solid (or liquid) phosphorus, forming the short-lived molecules HPO and P2O2 that both emit visible light. The reaction is slow and only very little of the intermediates is required to produce the luminescence, hence the extended time the glow continues in a stoppered jar.

Although the term phosphorescence is derived from phosphorus, the reaction which gives phosphorus its glow is properly called luminescence (glowing by its own reaction, in this case chemoluminescence), not phosphorescence (re-emitting light that previously fell on it).

[edit] Isotopes

Radioactive isotopes of phosphorus include

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