Selenium, Tellurium and Polonium

We have already noted that the properties of the elements in Group VI show the characteristic trends that we have come to expect on descending a Group. The elements become more metallic in character oxygen is a covalently bonded gaseous diatomic molecule sulfur is a solid containing Sg molecules and is an insulator selenium (non-metal) and tellurium (semi-metal) are semiconductors with polymeric structures polonium is a metal. The compounds of selenium, tellurium and pollonium also illustrate the inert pair effect and a tendency to higher coordination numbers. 

The halides formed by selenium, tellurium and polonium are summarized in Table 12.5. Table 12.5 The halides of selenium, tellurium and polonium 

It should be remembered that polonium is a rather rare element, which is difficult to handle because of its radioactivity because of this its chemistry has not been as fully explored as that of selenium and tellurium. 

We see the inert pair effect increasing down the Group as the stability of oxidation number +4 increases. All four tetrahalides exist for tellurium and polonium, but not for selenium. 

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K. W. BagnaH, The Chemistry of Selenium, Tellurium, and Polonium, 2nd ed., Elsevier Publishing Co., Amsterdam, the Netherlands, 1966. 

K. W. Bagnall, Selenium, tellurium and polonium. Chap. 24 in Comprehensive Inorganic Chemistry, Vol. 2, pp. 935-1008, Pergamon Press, Oxford, 1973. 

Selenium, tellurium, and polonium have not been as well studied as oxygen and sulfur, but they are known to form several long chains of atoms. Different lengths and arrangements of the chains cause differences in the way the elements look and react. 

Sulfur, selenium, tellurium and polonium constitute the heavier elements of group VIB of the periodic table and are sometimes referred to as the chalcogens, chalcogenins, chalcogenides or chalconides. Developments in the understanding and interest in the chemistry of these elements have been reviewed at appropriate intervals during the past 20 years.1-8... 

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

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