Phosphorus black allotropes

White phosphorus is very reactive. It has an appreciable vapour pressure at room temperature and inflames in dry air at about 320 K or at even lower temperatures if finely divided. In air at room temperature it emits a faint green light called phosphorescence the reaction occurring is a complex oxidation process, but this happens only at certain partial pressures of oxygen. It is necessary, therefore, to store white phosphorus under water, unlike the less reactive red and black allotropes which do not react with air at room temperature. Both red and black phosphorus burn to form oxides when heated in air, the red form igniting at temperatures exceeding 600 K,... 

Reactivity of white phosphorus is much greater than red or black phosphorus. Black phosphorus is the least reactive of all phosphorus allotropes. 

Black Phosphorus.—Another allotropic variety of phosphorus, distinguished by its black color, was discovered by TjjjSnard. To produce it, phosphorus is melted at ISO", and while in a state of fusion, is poured quickly into very cold water. 03ANM states that it may bo obtained also by passing ozonized... 

Figure 4 The structures of P4, white phosphorus (1) Hittorf s violet allotrope (2) Orthorhombic black allotrope (3) Rhombohedral black allotrope (4) showing the hexagonal arrangement and the distortion from planar the phosphides [Pis] (5), [P2i] (6) and...

Phosphoms exists in at least three allotropic forms. Allotropes are forms of an element with different physical and chemical properties. The three main allotropes are named for their colors white phosphorus (also called yellow phosphorus), red phosphorus, and black phosphorus (also called violet phosphorus). These allotropes have different physical and chemical properties. 

Two more stable phosphorus allotropes are red and black phosphorus. Small amounts of these are are also produced for special purposes from the white phosphorus product of the electric arc furnace. Red phosphorus is obtained by heating white phosphorus at 400°C for several hours, which yields a complex polymeric material, more dense (2.20 g/cm ) and considerably more stable than the white variety. Red phosphorus is not only stable in air, but far less toxic than white phosphorus. Black phosphorus is more dense again (2.25-2.69g/cm ), and has a different more complex structure. It is obtained by heating the white variety at 220 to 370°C for 8 days plus requires either a pressure exceeding 10 kg/cm or a seed crystal of black phosphorus. This product has a structure resembling graphite, is a good electrical conductor, and can be lit with a match only with difficulty [10] (Table 10.3). 

The white, red, and black allotropes of phosphorus have different properties. Note the differences in their structures. 

Arnauld Paul Edmond Thenard (Paris, 6 October 1819-Talmay, Cote d Or, 8 August 1884), son of the famous L. J. Thenard, baron, wealthy landowner in the Cote d Or and Saone et Loire, and interested mainly in agricultural chemistry, worked (partly with A. Thenard) on phosphorus hydrides, on ozone, the action of a silent electric discharge on gases, and a black allotropic form of phosphorus. In the determination of ozone he used the oxidation of a solution of arsenious oxide in hydrochloric acid. 

In the introduction we defined exotic as beautiful, exceptional, weird, paradoxical, and counterintuitive. We also indicated that such species could represent fragile and rare as well as simple and well-characterized classic inorganic compounds. In this section we will look at two of the simplest inorganic classes of compounds polyphosphorus and polynitrogen species. We will dwell on the following elementary question Why is it that polyphosphorus allotropes of the element are well known (white phosphorus black phosphorus in its orthorhombic, rhom-bohedral, and cubic forms red, amorphous phosphorus). 

The remaining forms of elemental phosphoms, namely black and red phosphorus, are insoluble polymers that are much less reactive than white phosphorus. Black orthorhombic phosphorus is the most thermodynamically stable form of this element and can be obtained by heating white phosphorus under pressure. Red phosphorus, in contrast to the black allotrope, is not crystalline but amor-... 

A third allotrope of phosphorus is black phosphorus. Black phosphorus is obtained by heating white phosphorus under pressure. This form of phosphorus is the most thermodynamically stable form, and therefore the least reactive. Black phosphorus has a layered structure similar to that of graphite. 

Phosphorus exists in four or more allotropic forms white (or yellow), red, and black (or violet). Ordinary phosphorus is a waxy white solid when pure it is colorless and transparent. White phosphorus has two modifications alpha and beta with a transition temperature at -3.8oC. 

The only element that was discovered in body fluids (urine). This is plausible, as P plays a main role in all life processes. It is one of the five elements that make up DNA (besides C, H, N, and 0 evolution did not require anything else to code all life). The P-O-P bond, phosphoric acid anhydride, is the universal energy currency in cells. The skeletons of mammals consists of Ca phosphate (hydroxylapatite). The element is encountered in several allotropic modifications white phosphorus (soft, pyrophoric P4, very toxic), red phosphorus (nontoxic, used to make the striking surface of matchboxes), black phosphorus (formed under high pressures). Phosphates are indispensable as fertilizer, but less desirable in washing agents as the waste water is too concentrated with this substance (eutrophication). It has a rich chemistry, is the basis for powerful insecticides, but also for warfare agents. A versatile element. 

Several allotropic forms of phosphorus are known, the most common of which are the white, red, and black forms. Heating the white form at 400 °C for several hours produces red phosphorus, which is known to include several forms. A red form that is amorphous can be prepared by subjecting white phosphorus to ultraviolet radiation. In the thermal process, several substances (I2, S8, and Na) are known to catalyze the conversion of phosphorus to other forms. Black phosphorus consists of four identifiable forms that result when white phosphorus is subjected to heat and pressure. Phosphorus is used in large quantities in the production of phosphoric acid and other chemicals. White phosphorus has been used extensively in making incendiary devices, and red phosphorus is used in making matches. 

Although phosphorus is in group 15 with some other metalloids, it is usually classed as a nonmetal since it resembles nitrogen somewhat, the element above it in group 15. Both are essential to the biochemical field as vital elements to support life. Phosphorus has 10 known allotropic forms. This is an unusually high number for any element. A system of categorizing the allotropes by three colors has made it easier to keep track of them. These three colors are white, red, and black phosphorus. 

Black phosphorus allotrope is produced by heating white phosphorus at 220°C under 12,000 atm pressure. The conversion is initially slow, but can became fast and explosive after an induction period. 

Investigation by X-ray methods 3 of the structure of samples of arsenolamprite from two different localities showed only partial agreement with that of metallic rhombohedral arsenic the differences may be attributed to the presence of impurity in the minerals, but could also be explained by the presence of a second allotropic modification corresponding to black metallic phosphorus (see p. 35). 

Four allotropes of phosphorus are known, the hexagonal /(-white, stable only below —77°C, the cubic a-white trap 44.1°C), the violet, and the black (which is thermodynamically the most stable). The a-white form is usually taken as the standard state. The violet is obtained by continued heating at 500°C of a solution of phosphorus in lead. When a-white phosphorus is heated to 250 C in the absence of air, a red variety (rap 590CC) is obtained which is believed to consist of a mixture of the a-white and violet allotropes, although the studies of the violet component in the mixture have shown that at least four polymorphic forms of red (violet) phosphorus exist. 

A review of the alleged allotropes of phosphorus reduces their number to four, namely, the a- and/3-forms of yellow phosphorus, red or violet phosphorus, and black phosphorus. Most of the work of various investigators has been directed towards elucidating the nature of red phosphorus, and of the transformation of yellow to red phosphorus and conversely. Red phosphorus was formerly considered to be amorphous, and it was often called amorphous phosphorus. The term amorphous, however, here referred more to the general appearance of the powder rather than to its minute structure. J. W. Retgers 5 showed that the particles of ordinary red phosphorus are rhombohedral crystals, which are well developed in those of W. Hittorf s violet phosphorus. All four varieties are therefore crystalline. J. W. Terwen has reviewed this subject in a general way and M. Copisarow discussed the theory of allotropy,... 

Elemental phosphorus itself exists in several polymeric forms. If the white allotropic form, which consists of P4 tetrahedral molecules, is put under high pressure, preferably at elevated temperatures, it can be catalytically converted to other modifications.41 It first becomes red, then violet, then black as the degree of polymerization increases. These materials are very difficult to characterize because of branching and the formation of cyclics. In the extreme limit, the structure approaches that of graphite, and shows good electrical conductivity.42 No evidence exists at all for the formation of high-molecular-weight, linear chains of elemental phosphorus. 

There are three allotropic forms of elemental phosphorus white, red, and black phosphorus. At room temperature, pure white phosphorus is a tetrahedral crystal with a molecular formula of P4. In the pure form, white phosphorus is an ivory-colored, waxy solid. The commercial product is 99.9% pure and may have a slightly yellow color. In the literature, the commercial product is often referred to as yellow phosphorus. In this chapter, the terms white phosphorus and phosphorus are used to refer to P4, which includes white and yellow phosphorus. 

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). 

Yellow forms of arsenic and antimony (the latter very unstable) have been described. These are presumably the nonmetallic modifications of these elements, analogous to white phosphorus, and also consisting of discrete molecules (tetrahedral quartets) in the solid state. The grey or metallic forms of arsenic and antimony are the most stable. They are far denser than the yellow forms, are insoluble in organic solvents, and have appreciable electrical conductivities. Black amorphous forms of arsenic and antimony are also known, and an additional allotrope of antimony, explosive (but always impure), has been described. 

Phosphorus exhibits allotropy, and formerly was thought to exist in two forms, yellow and red. In addition, several other varieties, scarlet, violet, metallic and black phosphorus, were discovered later, some of which are perhaps not to be regarded as true allotropes. Their properties will be considered partly in the present chapter, and partly in Chapter III. 

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