Group VI/16 elements

The usual acceptor and donor dopants for Al Ga As compounds are elements from groups II, IV and VI of the periodic table. Group II elements are acceptors and group VI elements are donors. Depending on the growth conditions. Si and Ge can be either donors or acceptor, i.e. amphoteric. This is of special interest in LEDs. 

All Group VI elements form a hydride HjX. With the notable exception of water, they are all poisonous gases with very unpleasant smells. Table 10.2 gives some of their important physical properties. 

Ethylene oxide (qv) was once produced by the chlorohydrin process, but this process was slowly abandoned starting in 1937 when Union Carbide Corp. developed and commercialized the silver-catalyzed air oxidation of ethylene process patented in 1931 (67). Union Carbide Corp. is stiU. the world s largest ethylene oxide producer, but most other manufacturers Hcense either the Shell or Scientific Design process. Shell has the dominant patent position in ethylene oxide catalysts, which is the result of the development of highly effective methods of silver deposition on alumina (29), and the discovery of the importance of estabUshing precise parts per million levels of the higher alkaU metal elements on the catalyst surface (68). The most recent patents describe the addition of trace amounts of rhenium and various Group (VI) elements (69). 

The metals of group Ilb (Zn, Cd, Hg) have low vaporization temperatures (Zn 907°C, Cd 756°C, Te 990°C). This favors the reaction of the vaporized metal with an alkyl of the group VI element at a temperature range of325-350°C, as shown in the following examples ... 

With phosphorus trichloride, a rather complex reaction results partly in the formation of [PhaP N uPPha PPhCl]+ Cl. The reactivity of the phosphorus(iii) atom is also demonstrated by its ability to desulphurize thiophosphoryl chloride, and its ready reactions with Group VI elements, diborane, and carbon disulphide ... 

Work of several types has been carried out. As long ago as 1970 Strom and Norton studied electron-withdrawal by substituents containing Group IV and Group VI elements through their effect on ESR methyl hyperfine splitting in l-phenyl-1,2-propanesemidiones 39. 

Ans. SF6, SF4, and SF2. The oxidation states of sulfur in these compounds correspond to the maximum oxidation state for a group VI element and to states 2 and 4 lower. (See Fig. 13-1.)... 

All five of the Group VI elements have a property called allotropy, which means they exist in more than one solid form. Like carbon, which could be black graphite or a sparkling diamond, these elements can exist with their atoms arranged in more than one way. 

The Group VI elements have six electrons in their outer shells. They combine most often by picking up two extra electrons to form a negative ion such as S 2. They can also combine by sharing electrons. 

Table 15.2 Properties of Hydrogen Compounds of Group VI Elements. ...

In the actinide compounds with the other group VI elements (X = S, Se, Te), the X/ An ratio varies from 1 to 3. These actinide chalcogenides show predominantly the composition AnX (cub.), AngXt (cub., orthorh.), AngXs (orthorh.), AnX2 (tetr.) and AnXg (orthorh.) which is also the order of decreasing thermal stability. 

There is a selenide Ga2Se3 and a telluride Ga2Te3, and materials can be synthesized which contain two of the group VI elements, e.g. Ga2S2Te. This compound contains GaS3Te units linked to give parallel chains Ga—S and Ga—Te distances are 230.7-235.3 and 255.6pm, respectively.591... 

Sulfur, Selenium, Tellurium and Polonium Table 1 Compounds of Group VI Elements and their Stereochemistries... 

It seems likely that the stable value of the dihedral angle for group VI elements is in general about 102°, and that the barrier (at 180°) is about 2 or 3 kcal/mole. The value 0.32 kcal/mole reported for H20 by microwave spectroscopy70 seems small in comparison with the values discussed above, although some decrease, perhaps 50 percent, might be expected because of the partial ionic character of the O—H bonds. 

B. Preparation of a Quadruple Bond Between Group VI Elements. 220... 

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