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Elemental phosphorus can exist in several allotropes, the most common of which are white and red solids. Solid violet and black allotropes are also known. Gaseous phosphorus exists as diphosphorus and atomic phosphorus. White phosphorus White phosphorus, yellow phosphorus or simply tetraphosphorus (P4) exists as molecules of four phosphorus atoms in a tetrahedral structure, joined by six phosphorus—phosphorus single bonds. The tetrahedral arrangement results in ring strain and instability. Although both are called "white phosphorus", in fact two different crystal allotropes are known, interchanging reversibly at 195.2 K. The element's standard state is the body-centered cubic α form, which is actually metastable under standard conditions. The β form is believed to have a hexagonal crystal structure. Molten and gaseous white phosphorus also retains the tetrahedral molecules, until 800 °C (1,500 °F; 1,100 K) when it starts decomposing to P2 molecules. The P4 molecule in the gas phase has a P-P bond length of rg = 2.1994(3) Å as was determined by gas electron diffraction. The β form of white phosphorus contains three slightly different P4 molecules, i.e. 18 different P-P bond lengths — between 2.1768(5) and 2.1920(5) Å. The average P-P bond length is 2.183(5) Å. White phosphorus is a translucent waxy solid that quickly yellows in light, and impure white phosphorus is for this reason called yellow phosphorus. It glows greenish in the dark (when exposed to oxygen) and is highly flammable and pyrophoric (self-igniting) upon contact with air. It is toxic, causing severe liver damage on ingestion and phossy jaw from chronic ingestion or inhalation. The odour of combustion of this form has a characteristic garlic smell, and samples are commonly coated with white "diphosphorus pentoxide", which consists of P4O10 tetrahedral with oxygen inserted between the phosphorus atoms and at their vertices. White phosphorus is only slightly soluble in water and can be stored under water. Indeed, white phosphorus is safe from self-igniting when it is submerged in water; due to this, unreacted white phosphorus can prove hazardous to beachcombers who may collect washed-up samples while unaware of their true nature. P4 is soluble in benzene, oils, carbon disulfide, and disulfur dichloride. Production and applications The white allotrope can be produced using several methods. In the industrial process, phosphate rock is heated in an electric or fuel-fired furnace in the presence of carbon and silica. Elemental phosphorus is then liberated as a vapour and can be collected under phosphoric acid. An idealized equation for this carbothermal reaction is shown for calcium phosphate (although phosphate rock contains substantial amounts of fluoroapatite): 2 Ca3(PO4)2 + 6 SiO2 + 10 C → 6 CaSiO3 + 10 CO + P4 White phosphorus has an appreciable vapour pressure at ordinary temperatures. The vapour density indicates that the vapour is composed of P4 molecules up to about 800 °C. Above that temperature, dissociation into P2 molecules occurs. In base, white phosphorus spontaneously disproportionates to phosphine and various phosphorus oxyacids. It ignites spontaneously in air at about 50 °C (122 °F), and at much lower temperatures if finely divided (due to melting-point depression). Phosphorus reacts with oxygen, usually forming two oxides depending on the amount of available oxygen: P4O6 (phosphorus trioxide) when reacted with a limited supply of oxygen, and P4O10 when reacted with excess oxygen. On rare occasions, P4O7, P4O8, and P4O9 are also formed, but in small amounts. This combustion gives phosphorus(V) oxide: P4 + 5 O2 → P4O10 Because of this property, white phosphorus is used as a weapon. Phosphorus pentachloride is prepared by the reaction of white phosphorus with excess of dry chlorine. P4 + 10Cl2 → 4PCl5 It can also be prepared by the action of sulfuryl chloride on white phosphorus. P4 + 10SO2Cl2 → 4PCl5 + 10SO2 Non-existence of cubic-P8 Although white phosphorus converts to the thermodynamically more stable red allotrope, the formation of the cubic-P8 molecule is not observed in the condensed phase. Analogs of this hypothetical molecule have been prepared from phosphaalkynes. White phosphorus in the gaseous state and as waxy solid consists of reactive P4 molecules. Red phosphorus Red phosphorus may be formed by heating white phosphorus to 300 °C (570 °F) in the absence of air or by exposing white phosphorus to sunlight. Red phosphorus exists as an amorphous network. Upon further heating, the amorphous red phosphorus crystallizes. Bulk red phosphorus does not ignite in air at temperatures below 240 °C (460 °F), whereas pieces of white phosphorus ignite at about 30 °C (86 °F). Under standard conditions it is more stable than white phosphorus, but less stable than the thermodynamically stable black phosphorus. The standard enthalpy of formation of red phosphorus is −17.6 kJ/mol. Red phosphorus is kinetically most stable. It was first presented by Anton von Schrötter before the Vienna Academy of Sciences on December 9, 1847, although others had doubtlessly had this substance in their hands before, such as Berzelius. Applications Red phosphorus can be used as a very effective flame retardant, especially in thermoplastics (e.g. polyamide) and thermosets (e.g. epoxy resins or polyurethanes). The flame retarding effect is based on the formation of polyphosphoric acid. Together with the organic polymer material, these acids create a char that prevents the propagation of the flames. The safety risks associated with phosphine generation and friction sensitivity of red phosphorus can be effectively minimized by stabilization and micro-encapsulation. For easier handling, red phosphorus is often used in form of dispersions or masterbatches in various carrier systems. However, for electronic/electrical systems, red phosphorus flame retardant has been effectively banned by major OEMs due to its tendency to induce premature failures. One persistent problem is that red phosphorus in epoxy molding compounds induces elevated leakage current in semiconductor devices. Another problem was acceleration of hydrolysis reactions in PBT insulating material. Red phosphorus can also be used in the illicit production of methamphetamine and Krokodil. Red phosphorus can be used as an elemental photocatalyst for hydrogen formation from the water. They display a steady hydrogen evolution rates of 633 μmol/(h⋅g) by the formation of small-sized fibrous phosphorus. Violet or Hittorf's phosphorus Monoclinic phosphorus, or violet phosphorus, is also known as Hittorf's metallic phosphorus. In 1865, Johann Wilhelm Hittorf heated red phosphorus in a sealed tube at 530 °C. The upper part of the tube was kept at 444 °C. Brilliant opaque monoclinic, or rhombohedral, crystals sublimed as a result. Violet phosphorus can also be prepared by dissolving white phosphorus in molten lead in a sealed tube at 500 °C for.... Discover the Violet Zhang popular books. Find the top 100 most popular Violet Zhang books.