Metalloid, definition

Control of metalloid content in natural objects, foodstuff and pharmaceuticals is an important task for modern analytical chemistry. Determination of elements such as Arsenic is necessary for evaluation of object toxicity, since their content in environment may exceed MCL (maximum contaminant level), posing hazard to human health. Elements such as Selenium in definite doses are healthy, but in greater quantities they produce toxic effect. 

The elements show increasing metallic character down the group (Table 14.6). Carbon has definite nonmetallic properties it forms covalent compounds with nonmetals and ionic compounds with metals. The oxides of carbon and silicon are acidic. Germanium is a typical metalloid in that it exhibits metallic or nonmetallic properties according to the other element present in the compound. Tin and, even more so, lead have definite metallic properties. However, even though tin is classified as a metal, it is not far from the metalloids in the periodic table, and it does have some amphoteric properties. For example, tin reacts with both hot concentrated hydrochloric acid and hot alkali ... 

Since the large majority of metalloid clusters E Rthis section is divided in two parts, including the few clusters for In hitherto known. For many of the metalloid clusters discussed in this section (for a definition of metalloid cf. Section 2.3.1, Introduction) the technique of cryochemistry is essential, i.e., trapping of a high-temperature species together with an excess of a suitable solvent in order to obtain a metastable solution. Detailed descriptions and discussions of this technique have been presented recently [7-12],... 

The nature of the substituents in the compounds containing metalloids in the ligand (N 20-22, Table 4) influences the absorption and photoconductivity spectra. The phosphorus atom interrupts the conjugation along the monomeric link. In contrast, the arsenic atom promotes the conjugation. One can assume the more definite dissociation of n-d bonds in the latter compounds compared with the usual acetylenides. 

The elements show increasing metallic character down the group (Table 14.12). Carbon has definite nonmetallic properties it forms covalent compounds with nonmetals and ionic compounds with metals. The oxides of carbon and silicon are acidic. Germanium is a typical metalloid... 

Is tetramethyldiarsine an organometallic compound By definition, arsenic is a so-called metalloid or semi-metal , not a metal, and thus organoarsenic compounds like the organic compounds of boron or silicon are not per se organometallics. There is no doubt that the preparation of tetramethyldiarsine and the elucidation of its structure may in retrospect be linked to the development of organometallic chemistry, but it would be far beyond the scope of this book, if the chemistry of the organic compounds of the metalloids in its entirety was discussed. 

A cross-coupling reaction can be partially defined by equation (1), where Nu is a carbon (or heteroatom) nucleophile see Nucleophile), R X is an electrophilic substrate, X is a halogen or other appropriate leaving group, and M is a metal or metalloid. At first glance, it would appear that simple nucleophihc substitution reactions should fall under this definition. However, what makes the cross-coupling chemistry special is its ability to perform transformations that cannot be accomplished with simple substitution chemistry. 

Over the past 30-1- years, cross-coupling protocols utilizing a wide variety of metals and metalloids have been studied. However, we will cover only those that have been applied the most often in organic synthesis. Furthermore, the related Heck (see Heck Reaction) and Tsuji-Trost reactions, which follow different mechanisms (and hence, do not fall under our more narrow definition), are beyond the scope of this entry. 

The more comprehensive definitions have grown to include metalloids and even what were considered only a few decades ago to be nonmetals. Furthermore, some are of the opinion that the so-called metals need not always be attached formally to carbon in order to have compounds with organometallic characteristics. An extreme case is the concept that carbon itself may partake of the characteristics of a metal and on such a classification simple compounds such as ethane or benzene are in and of themselves, organometallic compounds. 

In [6.41-43] we find reports of the experimental investigations of partial distribution functions of atoms in amorphous alloys. The strong LO is discovered in the alloys of the metal-metalloid and metal-metal types. The compositional order is closely (but not always unambiguously) connected with the topological order, so that the presence of the former testifies to the existence of the definite local topological order. 

The term speciation refers to the determination of the chemical form of metals and metalloids and according to lUPAC it is the process yielding evidence of the atomic or molecular form and oxidation state of an analyte. Included in this definition are the organometallic compounds and those of N, P, S and Si. The determination of organic substances is not referred to. 

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