Sulfur trioxide, selenium tellurium

Tellurium burns in air with a greenish-blue flame. The combustion product is dioxide, Te02, the most stable oxide of the metal. Tellurium also forms other oxides the monoxide, TeO, the trioxide, TeOs, and the pentoxide, Te205. Monoxide has not yet been obtained in solid form. Like sulfur and selenium, tellurium forms oxyacids. Such oxyacids include orthotelluric acid, HeTeOe and tellurous acid, H2Te03, in which the metal is in +6 and +4 valence states respectively. 

In Group VIA (16) the same phenomenon is encountered. Selenium trioxide is thermodynamically unstable relative to sulfur trioxide and tellurium trioxide. The enthalpies of formation of SF6, SeF6, and TeFft are -1210. — 1117, and — 1320 kj mol 1, respectively. This indicates comparable bond energies for S—F and Te—F bonds (317 and 330 kj mol-1, respectively), which are more stable than Se—F bonds (285 kj mol 1). 

Tellurium Halides. Tellurium forms the dihalides TeCl and TeBi, but not Tel2. However, it forms tetrahalides with all four halogens. Tellurium decafluoride [53214-07-6] and hexafluoride can also be prepared. No monohalide, Te2X2, is believed to exist. Tellurium does not form well-defined oxyhalides as do sulfur and selenium. The tellurium halides show varying tendencies to form complexes and addition compounds with nitrogen compounds such as ammonia, pyridine, simple and substituted thioureas and anilines, and ethylenediamine, as well as sulfur trioxide and the chlorides of other elements. 

The species, SeJ and TeJ, appear to be square-planar like whose similarity is supported by theoretical calculations that treat all of them as 6-ir electron systems.The yellow selenium cation is obtained by treating elemental selenium with fluorosulfuric acid, fuming sulfuric acid, sulfur trioxide, disulfuric acid, or antimony pentafluoride. The red tellurium cation is obtained simi-larly. = ... 

Polonium is a radioactive element that is difficult to study in the laboratory.) Oxygen has a tendency to accept two electrons to form the oxide ion (O ) in many ionic compounds. Sulfur, selenium, and tellurium also form dinegative anions (S, Se, and Te ). The elements in this group (especially oxygen) form a large number of molecular compounds with nonmetals. The important compounds of sulfur are SO2, SO3, and H2S. Sulfuric acid is formed when sulfur trioxide reacts with water ... 

Sulfur trioxide is produced from the catalytic oxidation of the dioxide. Its trigonal planar structure requires three resonance structures to describe. The very short S-0 bond distances seem to indicate that there are strong dir-fm interactions in addition to the expected delocalized fnr bonds. It is a powerful oxidizing agent. Although selenium and tellurium are less stable in the +6 oxidation state than is sulfur, both Se03 and Te03 can be prepared. 

The electrochemical behaviour of silver, mercury, gold, platimmi and vitreous carbon electrodes was examined in chlorosulfonic acid the experiments showed that only the latter material was not attacked the oxidizing properties of chlorosulfonic acid were mainly due to the presence of sulfur trioxide/ As mentioned in Chapter 1, chlorosulfonic acid reacts with powdered selenium or tellurium with the formation of moss-green or cherry-red colours respectively, which may be used as spot tests for the reagent/... 

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. 

Trioxides of sulfur, selenium, and tellurium are well recognized, but polonium trioxide has yet to be prepared in weighable quantities. 

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