Boron elemental arsenic

Boron and arsenic are natural components of soil and are both present as oxyanions. Boron is present as boric acid or borate polymers, and arsenic is present as arsenate. While boron is weakly held by soil, arsenic is similar to phosphate in its interactions with soil constituents. Boron is an essential nutrient for plants however, it is also toxic to plants at relatively low levels. Arsenic is toxic. The laboratory chemistry of both of these elements is well understood, but their environmental chemistry, speciation and movement, is less well understood [23-27],... 

Sihcon of hyperpurity, doped with trace elements, such as boron, phosphorus, arsenic, and gadium is one of the best semiconductors. They are used in transistors, power rectifiers, diodes and solar ceds. Sihcon rectifiers are most efficient in converting a-c to d-c electricity. Hydrogenated amorphous sihcon converts solar energy into electricity. 

In this section we describe some exotic applications of the bioisostery concept implying the utilization of unusual elements such as silicon, boron, selenium, arsenic, and antimony. The use of those elements as bioisosteres of carbon in existing drugs is a different approach enabling the introduction of a new drug-like chemical space into the drug discovery and development process. 

The term metalloid was introduced by Erman and Simon in 1802 to indicate such elements as possess metallic physical properties, but non-metallic chemical properties. These include boron, silicon, arsenic, antimony, selenium and tellurium. Sometimes iodine is added to the list. Unfortunately in 1811 Berzelius employed the term metalloid as synonymous with non-metal and at the present time the French still adhere to its use in that sense. In the present chapter we shall deal with boron and silicon only. 

In this section we describe some exotic applications of the bioisostery concept implying the utilization of unusual elements, such as silicon, boron, selenium, arsenic and antimony. 

Ion implantation [15] forces ions of dopant into the silicon using a stream of high energy ions produced in a machine similar to a mass spectrophotometer. Sources of dopants for this process are elemental arsenic and phosphorus, arsine, phosphine, diborane, and some boron halides. A more detailed description of doping procedures is beyond the scope of this text and can be found elsewhere [8]. 

Thousands of compounds of the actinide elements have been prepared, and the properties of some of the important binary compounds are summarized in Table 8 (13,17,18,22). The binary compounds with carbon, boron, nitrogen, siUcon, and sulfur are not included these are of interest, however, because of their stabiUty at high temperatures. A large number of ternary compounds, including numerous oxyhaUdes, and more compHcated compounds have been synthesized and characterized. These include many intermediate (nonstoichiometric) oxides, and besides the nitrates, sulfates, peroxides, and carbonates, compounds such as phosphates, arsenates, cyanides, cyanates, thiocyanates, selenocyanates, sulfites, selenates, selenites, teUurates, tellurites, selenides, and teUurides. 

Instead of depending on the thermally generated carriers just described (intrinsic conduction), it is also possible to deUberately incorporate various impurity atoms into the sihcon lattice that ionize at relatively low temperatures and provide either free holes or electrons. In particular. Group 13 (IIIA) elements n-type dopants) supply electrons and Group 15 (VA) elements (p-type dopants) supply holes. Over the normal doping range, one impurity atom supphes one hole or one electron. Of these elements, boron (p-type), and phosphoms, arsenic, and antimony (n-type) are most commonly used. When... 

Silicon s atomic structure makes it an extremely important semiconductor. Highly purified silicon, doped with such elements as boron, phosphorus, and arsenic, is the basic material used in computer chips, transistors, sUicon diodes, and various other electronic circuits and electrical-current switching devices. Silicon of lesser purity is used in metallurgy as a reducing agent and as an alloying element in steel, brass, and bronze. 

These studies show that radon can be classified as a metalloid element, together with boron, silicon, germanium, arsenic, antimony, tellurium, polonium, and astatine. Like these elements, radon lies on the diagonal of the Periodic Table between the true metals and nonmetals (Figure 5) and exhibits some of the characteristics of both (Stein, 1985). 

Atomic absorption spectrometric methods and, more recently, the inductively coupled plasma atomic emission method, are, of course, mandatory if determination of elements is required (arsenic, selenium, boron, phosphorus and silicon). 

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