Chemical properties of selenium

The chemical properties of selenium fall between sulfur and tellurium. Thus, selenium reacts with oxygen similarly to sulfur, forming two oxides, selenium dioxide, Se02 and trioxide, SeOs. The metal combines with halogens forming their halides. With nonmetals, selenium forms binary compounds exhibiting oxidation states +4 and -i-6. 

Physical and Chemical Properties of Selenium and Selenium Compounds... 

Chapter 4 has more information on the physical and chemical properties of selenium and its compounds. Chapter 5 provides more information on the sources and uses of selenium. 

Although the differences in physical and chemical properties of selenium and sulfur tend to separate these elements in weathering and erosion, their similar functions in biological reactions tend to unite them in organic-rich materials. Selenium is found often manyfold its crustal abundance in black organic-rich shales, in coal, and, to a lesser extent, in petroleum. 

Group VIA, like the preceding groups, shows the trend from nonmetallic to metallic as you proceed from top to bottom of the column of elements. Oxygen and sulfur are strictiy nonmetallic. Although the chemical properties of selenium and tellurium are predominantly those of nonmetals, they do have semiconducting allotropes as expected of metalloids. Polonium is a radioactive metal. 

Chemical Properties. The most significant chemical property of L-ascorbic acid is its reversible oxidation to dehydro-L-ascorbic acid. Dehydro-L-ascorbic acid has been prepared by uv irradiation and by oxidation with air and charcoal, halogens, ferric chloride, hydrogen peroxide, 2,6-dichlorophenolindophenol, neutral potassium permanganate, selenium oxide, and many other compounds. Dehydro-L-ascorbic acid has been reduced to L-ascorbic acid by hydrogen iodide, hydrogen sulfide, 1,4-dithiothreitol (l,4-dimercapto-2,3-butanediol), and the like (33). 

Consider the proper placement of tellurium and iodine in the periodic table, as shown in Figure 1-3. Te has the heavier atomic weight. The chemical properties of tellurium are like those of selenium because both are semi-metallic elements that form compounds like those of sulfur. Iodine resembles bromine because these elements are nonmetallic halogens that form compounds like those of chlorine. Therefore, the order in the table cannot be based solely on atomic weight. 

As in the case of sulphur, XPS was most suitable for studying electron transport on protein bound selenium, especially in those reactions where no magnetic properties or electronic transitions can be measured The chemical shift of the binding energy values of the Se 3 d levels can reach up to 7.5 eV (Table 3). This large shift allows the assignment of the chemical nature of selenium and selenopeptides to be made Measurements of selenotrisulphides, the well known reaction products between selenite and thiols, deserved special attention (Table 4). 

Occurrence, Extraction and Purification—The Allotropy of Selenium—Colloidal Selenium—General Physical Properties of Selenium—Chemical Properties— Applications of Element—Physiological Action—Atomic Woighl—Valency— Constitution of Selenium Molecule—Detection and Estimation of Selenium. 

Chemical Constitution of Selenium Acetylacetone.—This compound is dimeric and devoid of enolic properties. It combines with acetylacetone to form selenium OC-6i acetylacetone,... 

Selenium is in group 16 of the periodic table and although it has chemical and physical properties intermediate between metals and nonmetals (Table 1), it is usually described as a nonmetal. The chemical behavior of selenium has some similarities to that of sulfur. Formally, selenium can exist in the —II, 0, IV, and VI oxidation states (Table 2). Selenium has six natural stable isotopes, the most important being Se and °Se. Although Se is generally also regarded as a stable isotope, it is a )8-emitter with a very long half-life (1.4 X 10 ° yr). Both arsenic and selenium tend to be covalently bonded in all of their compounds. 

The physico-chemical properties of the analytes and the way they reach the detector have made atomic spectroscopy the detection technique of choice in most instances. A heated quartz cell or a similar device is connected directly to the gas outlet of the separation cell [26]. The use of an atomic fluorescence detector has provided methods for selenium [25,27] and mercury [28,29] that possess excellent analytical features and use inexpensive instruments. On a less affordable level are ICP emission [30] and atomic emission cavity spectrometers [31]. 

Physical and Chemical Properties. The physical and chemical properties of elemental selenium and most of the common environmental forms of selenium have been characterized (Budavari et al. 1996 Lide 2000) and no further data are needed (see Chapter 4). 

The chemical properties of tellurium resemble that of selenium and sulfur, though it is more metallic than these elements. In air, tellurium burns with a greenish-blue flame, forming tellurium dioxide that is only sparingly soluble in water. Tellu-... 

Chemical Properties of Dextrose.—The reactions of dextrose are in accord with the formula which has been assigned to it. It reacts as an aldehyde with an ammoniacal solution of silver oxide, with Fehling s solution, and with alkalies. An alkaline solution of dextrose precipitates selenium, tellurium, gold, platinum, and certain other metals from their salts. 

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