Metalloids Arsenic, Antimony

Introduction Arsenic and antimony, like red phosphorus, vaporize more slowly than expected from their thermochemical properties. L vov and Novichikhin 

The refined results of this thermochemical analysis are given below. The thermodynamic functions required for the calculation are given in Table 16.3, and the theoretically calculated and experimentally measured enthalpies of the corresponding reactions, in Table 16.4. 

Results and Discussion The initial data for calculating the enthalpy by the third-law method were the equivalent pressures measured for both elements under the free-surface vaporization conditions (after Langmuir) in [8]. The quantities were also determined in [8] by the second-law method. 

Element T (K) Primary Products Peqp (bar) Equilibrium Products Peq (bar) (Xy Theory Expt Ref. 

7kJ moP. If so, the calculated enthalpy will increase to 178.2 kJ moP and the discrepancy will decrease to 3-6%. 

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Bentley R, TG Chasteen (2002) Microbial methylation of metalloids arsenic, antimony and bismuth. Microbiol Mol Biol Rev 66 250-271. 

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). 

Some of the metalloids are considered semiconductors. The term metalloids is used in this reference book because these elements do have characteristics of both metals and non-metals, and the term semiconductor refers only to particular elements somewhere between metals and nonmetals. Semiconductors also have properties of both metals and nonmetals. Therefore, they have the ability to act as conductors of electricity and thermal energy (heat), as well as the ability to act as insulators or nonconductors of electricity and heat, depending upon the kind and amount of impurities their crystals contain. Again, following the zigzag steps on the periodic table, the metalloids having properties of both metals and nonmetals are as follows boron, silicon, germanium, arsenic, antimony, tellurium, and polonium. 

The metal combines with sulfur and phosphorous on heating, forming the sulfide and phosphide salts, respectively. Metalloid elements, such as arsenic, antimony, selenium and tellurium also combine with indium at elevated temperatures, forming their respective binary salts. 

Semimetals Seven of the nine elements adjacent to the zigzag boundary between metals and nonmetals—boron, silicon, germanium, arsenic, antimony, tellurium, and astatine—are known as semimetals, or metalloids, because their properties are intermediate between those of their metallic and nonmetallic neighbors. Though most are silvery in appearance and all are solid at room temperature, semimetals are brittle rather than malleable and tend to be poor conductors of heat and electricity. Silicon, for example, is a widely used semiconductor, a substance whose electrical conductivity is intermediate between that of a metal and an insulator. 

In situations like these the method of measurement of the element (or elements) of interest can be tailored specifically to suit the particular needs. As a matter of fact, for a few metals like mercury and tin and the metalloids arsenic, selenium, antimony, and tellurium special methods of sample preparation are usually required (29,30,31,32,33). The reason special precautions and special methods are required for the elements listed above, and for certain others, is that they either are readily reduced to volatile forms, react chemically to form volatile compounds, or are influenced in their analysis by the matrices usually present. ... 

The poor metals among the BCNOs usually include aluminum, gallium, indium, thallium, tin, lead, and bismuth. The metalloids are boron, silicon, germanium, arsenic, antimony, tellurium, and polonium. The nonmetals are carbon, nitrogen, oxygen, phosphorus, sulfur and selenium. These groups are not official, and chemists sometimes disagree on whether a particular element like boron should be called a metal or a metalloid. 

The complex of tartaric acid and antimony (emetic) was described three centuries ago. Nevertheless, the structure of this compound has been elucidated these last fifteen years by X-ray diffraction ( 1 ). In fact, emetic presents a binuclear cyclic structure. Many authors mentioned similar complex with transition metals (vanadium (2), chromium (3)) or metalloids (arsenic (4), bismuth (5)). Emetic with phosphorus was not mentioned. Nevertheless, tartaric acid or alkyl tartrates has been utilized in phosphorus chemistry tartaric acid reacts with trialkyl phosphites giving heterocyclic phosphites (6). Starting from alkyl tartrates, we prepared spirophosphoranes with a P-H bond and sixco-ordinated compounds (7). With unprotected tartaric acid, many possibilities appear condensation as a diol, as a di(oc-hydro-xyacid), or even as a 8-hydroxyacid. 

Methods for several metals or metalloids involve conversion to a volatile form. Arsenic, antimony, and selenium can be reduced to their volatile hydrides, AsH3, SbH3, and H2Se, repectively, which can be determined by atomic absorption or other means. Mercury is reduced to volatile mercury metal, which is evolved from solution and measured by cold vapor atomic absorption. 

The metallic properties are most pronounced for elements in the lower left-hand corner of the periodic table, and the non-metallic properties are most pronounced for elements in the upper right-hand corner. The transition from metals to non-metals is marked by the elements with intermediate properties, which occupy a diagonal region extending from a point near the upper center to the lower right-hand corner. These elements, which are called metalloids, include boron, silicon, germanium, arsenic, antimony, tellurium, and polonium.. 

Group V, the nitrogen or phosphorus group Nitrogen and phosphorus are non-metals, and their congeners arsenic, antimony, and bismuth are metalloids. Tiie chemistry of nitrogen is described briefly... 

The members of group of the periodic table show the expected trend in properties with increasing atomic number (f able 21 1) nitrogen is a gas which can be condensed to a liquid only at very low temperatures phosphorus (in the modification called w I tilt phosphorus) is a low-melting non-metal and arsenic, antimony, and bismuth are metalloids with increasing metallic character. 

Class I. ELEMENTS. A. Metals. Cubic copper, silver, gold, iron, platinum, iridium. - Tetragonal tin. - Rhombohedral and Hexagonal arsenic, antimony, bismuth, tellurium, (Os, Ir). - B. Metalloids. Cubic diamond. - Hexagonal graphite. - Orthorhombic sulfur, iodine. - Monoclinic sulfur, selenium. - Class II. SULFIDES. - Class HI. HALIDES. -Class IV. OXIDES, divided into SIMPLE OXIDES and COMPLEX OXIDES, such as CARBONATES, PHOSPHATES, SILICATES, BORATES and SULFATES. 

The elements have been classified empirically based on similarities in their physical or chemical properties. Metals and nonmetals are distinguished by the presence (or absence) of a characteristic metallic luster, good (or poor) ability to conduct electricity and heat, and malleability (or brittleness). Certain elements (boron, silicon, germanium, arsenic, antimony, and tellurium) resemble metals in some respects and nonmetals in others, and are therefore called semimetals or metalloids. Their ability to conduct electricity, for example, is much worse than metals, but is not essentially zero like the nonmetals. 

The first two elements of Group 5A(15), gaseous nonmetallic nitrogen (N) and solid nonmetallic phosphorus (P) have great industrial, environmental, and biological significance. Below these nonmetals are two metalloids, arsenic (As) and antimony (Sb), followed by the sole metal, bismuth (Bi), the last nonradioactive element in the periodic table [Group 5A(15) Family Portrait]. 

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. 

The elements that lie close to the "stair-step" line in Figure 3.7 often show a mixture of metallic and nonmetallic properties. These elements, which are called metalloids or semimetals, include silicon, germanium, arsenic, antimony, and tellurium. 

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