White phosphorus properties

Black phosphorus is formed when white phosphorus is heated under very high pressure (12 000 atmospheres). Black phosphorus has a well-established corrugated sheet structure with each phos phorus atom bonded to three neighbours. The bonding lorces between layers are weak and give rise to flaky crystals which conduct electricity, properties similar to those ol graphite, it is less reactive than either white or red phosphorus. 

The commonest form of phosphorus, and the one which is usually formed by condensation from the gaseous or liquid states, is the waxy, cubic, white form o -P4 (d 1.8232 gcm at 20°C). This, paradoxically, is also the most volatile and reactive solid form and thermodynamically the least stable. It is the slow phosphorescent oxidation of the vapour above these crystals that gives white phosphorus its most characteristic property. Indeed, the emission of yellow-green light from the oxidation of P4 is one of the earliest recorded examples of chemiluminescence, though the details of the reaction... 

The element phosphorus forms a variety of allotropic forms in the solid state. In the chemistry stockroom, you are likely to find red phosphorus and possibly white phosphorus (Figure B). As you can see, white phosphorus has the molecular formula P4, whereas red phosphorus might be represented as Px, where x is a very large number. The difference in properties between the two allotropes reflects the difference in their bonding patterns, molecular versus network covalent ... 

The remaining four elements form molecular solids. The atoms of white phosphorus, sulfur, and chlorine are strongly bonded into small molecules (formulas, P4, S8, and Cl2, respectively) but only weak attractions exist between the molecules. The properties are all appropriate to this description. Of course there is no simple trend in the properties since the molecular units are so different. 

The use of white phosphorus (P4) is an exception to the rule of using the most stable form, since red phosphorus is more stable (but its properties are less reproducible). 

By far the most important redox reaction relative to chemical stability is the reaction between an oxidizable material and oxygen from air. The particle size and any droplets have a large effect on the combustion properties. Some substances react so rapidly in air that ignition occurs spontaneously. These so called pyrophoric compounds (white phosphorus, alkali metals, metal hydrides, some metal catalysts, and fully alkylated metals and nonmetals) must be stored in the absence of air. 

White phosphorus has a white waxy appearance that turns slightly yellow with age and impurities. There are two allotropic forms of white phosphorus. The alpha (a) form has a cubic crystal structure, and the beta (P) form has a hexagonal crystalline structure. White phosphorus is extremely reactive and will spontaneously burst into flame when exposed to air at a temperature of about 35°C. It must be kept under water. But this property of spontaneous combustion has made it useful for military applications. 

The allotropes of phosphorus may be identified from their physical properties. White phosphorus can be identified from its chemiluminescence (a pale... 

Arsenic exhibits allotropy, which is characteristic of non-metals the usual, more stable, metallic form resembles the typical metals in appearance and in being a fairly good conductor of electricity. Under atmospheric pressure it begins to volatilise at about 450° C. and passes into a vapour containing complex molecules, As4, which at higher temperatures dissociate to As2 this complexity is not unusual in non-metals. The yellow allotrope, which is stable at low temperatures, resembles white phosphorus in being soluble in carbon disulphide—a property which emphasises the non-metallic character of this variety. The reactivity of the allotropes, as in the case of phosphorus, differs considerably. 

These experts collectively have knowledge of white phosphorus s physical and chemical properties, toxicokinetics, key health end points, mechanisms of action, human and animal exposure, and quantification of risk to humans. All reviewers were selected in conformity with the conditions for peer review specified in Section 104(I)(13) of the Comprehensive Environmental Response, Compensation, and Liability Act, as amended. 

Physical Properties of Major Components in White Phosphorus Smoke... 

You will find more information on the physical properties and uses of white phosphorus and white phosphorus smoke in Chapters 3 and 4 of this profile. 

Lee et al. (1975) also qualitatively studied urinary metabolites of32P-labeled white phosphorus in rats. They used thin-layer chromatography (TLC) at 4 and 24 hours after a single oral dose to show that radioactive urinary metabolites consisted of two classes of compounds. One of the compounds corresponded to inorganic phosphate, the other compound was less polar and suggested an organic phosphate, although the composition of this class of metabolites was not determined. TLC analysis of liver extract also showed two classes of compounds with similar properties. 

A safer and potentially more reliable antagonist to white phosphorus dermal absorption is a solution of silver nitrate (AgN03). The mechanism is not known with certainty (Song et al. 1985) but is hypothesized to be formation of Ag3P, the toxic properties of which are not reported. 

Various lavage solutions have been suggested, including mineral oil, saline, and dilute copper sulfate solution. Dilute copper sulfate has been suggested for its emetic properties, as well as for its ability to form an apparently inert complex with phosphorus that reduces white phosphorus absorption (Eldad and Simon 1991 Summerlin et al. 1967). 

Elemental phosphorus exists in several allotropic forms (Van Wazer 1982). The best known and most important commercially is the a-white phosphorus whose properties are given in Table 3-2. Commercial white phosphorus is 99.9% pure, with a slight yellow color caused by traces of red phosphorus impurities. Hence, white phosphorus also is known as yellow phosphorus. When a-white phosphorus is cooled below -79.6°C, P-white phosphorus forms. Other important solid allotropes of phosphorus are red and black phosphorus (Van Wazer 1982). 

TABLE 3-2. Physical and Chemical Properties of White Phosphorus... 

Organic constituents that may be found in ppb levels in WP/F smoke include methane, ethylene, carbonyl sulfide, acetylene, 1,4-dicyanobenzene, 1,3-dicyanobenzene, 1,2-dicyanobenzene, acetonitrile, and acrylonitrile (Tolle et al. 1988). Since white phosphorus contains boron, silicon, calcium, aluminum, iron, and arsenic in excess of 10 ppm as impurities (Berkowitz et al. 1981), WP/F smoke also contains these elements and possibly their oxidation products. The physical properties of a few major compounds that may be important for determining the fate of WP/F smoke in the environment are given in Table 3-3. 

Table 3-3. Physical Properties of Major Compounds in White Phosphorus Smoke3... 

Because it is a mixture, the physical properties of red phosphorus are variable. Thus, the density ranges from 2.10 to 2.34, depending on the completeness of the transformation from the white to the violet allotrope. The vapor formed when red phosphorus is heated is identical with that formed by white phosphorus in either case, condensation of these vapors produces white phosphorus. The red modification is much less active chemically than the white variety and is insoluble in those solvents which dissolve white phosphorus. 

Red Phosphorus.—The chief chemical properties of red or amorphous phosphorus were determined by the discoverer and other early investigators. As compared with white phosphorus, both red and scarlet phosphorus are relatively inert, except in respect to certain reactions which depend largely on the extent of surface exposed to aqueous reagents. 

Properties Pale-yellowish, translucent, crystallizable solid of waxy consistency. Sp, gr, 1.82 at 20°. M. P. 44.1°. B. P. 280°. Spontaneously inflammable in air at normal temperature gives off dense white smoke, consisting of phosphorus pentoxide and phosphoric acid. The former has a very high obscuring power. White phosphorus has the greatest total obscuring power (T. 0, P.) of all smoke agents. 

Ores of phosphorus apatite, hydroxy-apatite, iricalcium phosphate (phosphate rock). White phosphorus, red phosphorus, black phosphorus. High polymers and their properties. Manufacture and uses of phosphorus. Ordinary matches, safety matches. 

All these properties allow us to regard liquid white phosphorus as a liquid which may freeze in various forms certain of these forms, as amorphous or crystallized white phosphorus, cannot exist at the relatively high temperatures which we consider as for the form red phosphorus, its point of fusion into the liquid white form, if it exists, is very much higher than the temperatures which we can reach at these temperatures the liquid white phoepharus should be considered as a liquid in surfusion with respect to the solid red phosphorus. 

---