Phosphorus elemental form

Chlorine reacts with most elements, both metals and non-metals except carbon, oxygen and nitrogen, forming chlorides. Sometimes the reaction is catalysed by a trace of water (such as in the case of copper and zinc). If the element attacked exhibits several oxidation states, chlorine, like fluorine, forms compounds of high oxidation state, for example iron forms iron(III) chloride and tin forms tin(IV) chloride. Phosphorus, however, forms first the trichloride, PCI3, and (if excess chlorine is present) the pentachloride PCI5. 

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 radius of an atom helps to determine how many other atoms can bond to it. The small radii of Period 2 atoms, for instance, are largely responsible for the differences between their properties and those of their congeners. As described in Section 2.10, one reason that small atoms typically have low valences is that so few other atoms can pack around them. Nitrogen, for instance, never forms penta-halides, but phosphorus does. With few exceptions, only Period 2 elements form multiple bonds with themselves or other elements in the same period, because only they are small enough for their p-orbitals to have substantial tt overlap (Fig. 14.6). 

Nitrogen is a colorless diatomic gas. Phosphorus has several elemental forms, but the most common is a red solid that is used for match tips. Arsenic and antimony are gray solids, and bismuth is a silvery solid. Classify these elements of Group 15 as metals, nonmetals, or metalloids. 

The most thermod3Tiamically stable form of the element is black phosphorus, which can be prepared by heating red phosphorus under high pressure. The black form contains chains of P4 units cross-linked by P—P bonds, making this form even more polymerized and less strained than red phosphoms. Example explores another difference between the elemental forms of phosphorus. 

There is no doubt that the element phosphorus occupies a special position in the family of the elements. The Earth s crust (including the oceans), which is about 16 km thick, contains only about 0.04% phosphorus, compared, for example, with 2.4% potassium however, phosphorus is present in all the substances necessary for living processes. It does not occur in elemental form because of its high affinity for oxygen and has been known since its discovery by the alchemist Henning Brand in Hamburg in the course of his search for the philosopher s stone. However, it was many years later that Antoine Lavoisier realized that this new, shining substance was a chemical element. 

The central importance of phosphorus and its derivatives in our world leads to the question as to where the element came from phosphorus compounds must have been present on the Earth after its formation, but we do not know their source. Were they already present in planetesimals, or was phosphorus brought to Earth from space (in an elemental form or as compounds) ... 

Elemental sulfur is a yellow solid, in which eight snlfnr atoms form a crown-shaped ring Ss. Unlike elemental white phosphorus, elemental snlfnr has very low toxicity. Years ago, people in the United States took a preparation of snlfnr and molasses as a spring tonic. Taken orally, sulfur has a mild laxative effect. Beyond that, it is not clear to me what favorable effects this tonic may have had, if any. There is a lot of snlfnr aronnd. When taken in all its forms, it accounts for nearly 2% of the weight of the crnst of the Earth. 

In the latter, the valency angles must be about 100°, so the layers cannot be flat. Their shape is obtained if, in Figure 38, the atoms shown with the clear circles are displaced somewhat below the plane of the paper and the shaded ones similarly, above it. If the layers formed in this way are then arranged on top of one another, the crystal structure of the elements arsenic, antimony and bismuth are obtained in their normal forms in which they have metallic properties. There also exists a modification of phosphorus with a similar structure. In addition, there are other forms of arsenic and antimony, the properties of which correspond to those of yellow phosphorus these forms contain molecules p As4 and Sb4. 

MOLECULE, hi the traditional sense, a molecule is the smallest particle of a chemical substance capable of independent existence with retention of all its chemical properties. Molecules comprise one or more atoms which need not be of the same kind. Only the rare, or noble gases form single-atom or monatomic molecules. All other elements form bi-. Iri. quudrt-. etc. atomic molecules, e.g.. hydrogen. H ozone. O-, phosphorus. P4 and sulfur, Sx or hydrogen chloride. IICI sodium sullide. Na S. aluminum chloride, AlClu carbon tetrachloride. C CI. and so on. 

Although many phosphorus-containing compounds are vital to life processes, as previously described, there are also many phosphorus compounds that axe quite toxic—elemental phosphorus, for example. While the elemental form is dangerous because of its low combustion temperature, its absorption also has an acute effect on the liver. The long and continued absorption of small amounts of phosphorus can result in necrosis of the mandible or jaw bone (sometimes called phossyjaw ). Chronic phosphorus poisoning occurs particularly through the lungs and... 

The polymers which have been used to illustrate problems of inorganic polymer formation have been lieteroatomic. that is, their chains are built from different atoms alternating with each other. The other structure mentioned has been homoatomic—all the atoms in the chain are the same. There aie only a few homoatomic polymers of airy promise. Most elements will form only cyclic materials of low molecular weight if they polymerize at all. In addition to the silane polymers, black phosphorus, a high-pressure modification of the element, forms in polymeric sheets. 

It is somewhat difficult to define what is meant by a toxic element. Some elements, such as white phosphorus, chlorine, and mercury, are quite toxic in the elemental state. Others, such as carbon, nitrogen, and oxygen, are harmless as usually encountered in their normal elemental forms. But, with the exception of those noble gases that do not combine chemically, all elements can form toxic compounds. A prime example is hydrogen cyanide. This extremely toxic compound is formed from three elements that are nontoxic in the uncombined form, and produce compounds that are essential constituents of living matter, but when bonded together in the simple HCN molecule constitute a deadly substance. 

The most common elemental form of phosphorus, white phosphorus, is highly toxic. White phosphorus (melting point (mp), 44°C boiling point (bp), 280°C) is a colorless waxy solid, sometimes with a yellow tint. It ignites spontaneously in air to yield a dense fog of finely divided, highly deliquescent P4O10 ... 

Another nonmetal for which a method of determining biological exposure would be useful is white phosphorus, the most common and relatively toxic elemental form. Unfortunately, there is not a chemical method suitable for the determination of exposure to white phosphorus that would distinguish such exposure from relatively high background levels of organic and inorganic phosphorus in body fluids and tissues. 

Different elective affinity of elements as compared to carbon. Electropositive elements (Si, B, AI, P) have a considerably larger affinity to electronegative elements than carbon. In other words, silicon, boron, aluminum, phosphorus and other elements form weaker bonds with electropositive elements (H, Si, B, Al, As, Sb, Bi, etc.), and stronger bonds with electronegative elements (O, N, Cl, Br, F, etc.) than carbon. 

Arylation at phosphorus has also been reported in triphenylphosphine best yields of phosphonium salts were obtained under photochemical conditions [94], Metals were also arylated, either in their elemental form, such as bismuth, or in organometallics containing iron, iridium, etc. [1,2]. 

Note that nitrates have three oxygen atoms surrounding each nitrogen whereas phosphates have four oxygens about each phosphorus. This is probably not a radius ratio effect but is instead connected with the inability of phosphorus to form double bonds of the usual type. When nitrogen, a first-row element, forms four bonds, one or two may be double, but when phosphorus forms four bonds, all must be single. A number of workers feel that there is some overlap between the 3d orbitals of phosphorus and the 2p orbitals of oxygen in phosphates, and that this leads to double-bond character" of a sort, but this question is still open. 

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