The Group 6A Elements

The Group 6A elements can form covalent bonds with other nonmetals. For example, they combine with hydrogen to form a series of covalent hydrides of the general formula H2X. Those members of the group that have valence d orbitals available (all except oxygen) commonly form molecules in which they are surrounded by more than eight electrons. Examples are SF4, SFg, TeG, and SeBr4. 

The two heaviest members of Group 6A can lose electrons to form cations. Although they do not lose all six valence electrons because of the high energies that would be required, tellurium and polonium appear to exhibit some chemistry involving their 4+ cations. ITowever, the chemistry of these Group 6A cations is much more limited than that of the Group 5A elements bismuth and antimony. 

Polonium was discovered in 1898 by Marie and Pierre Curie in their search for the sonrces of radioactivity in pitchblende. Polonium has 27 isotopes and is highly toxic and very radioactive. It has been suggested that the isotope °Po, a natural contaminant of tobacco and an a-particle producer (see Section 20.1), might be at least partly responsible for the incidence of cancer in smokers. 

Selected Physical Properties, Sources, and Methods of Preparation of the Group 6A Elements 

Element Electronegativity Radius of (pm) Source Method of Preparation 

Sulfur 2.6 184 Sulfur deposits Melted with hot water and pumped to the surface 

Selenium 2.6 198 Impurity in sulfide ores Reduction of H2Se04 with SOj 

Tellurium 2.1 221 Nagyagite (mixed sulfide and telluride) Reduction of ore with SOj 

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The group 6A elements are oxygen, sulfur, selenium, tellurium, and polonium. As shown in Table 19.7, their properties exhibit the usual periodic trends. Both oxygen and sulfur are typical nonmetals. Selenium and tellurium are primarily non-metallic in character, though the most stable allotrope of selenium, gray selenium, is a lustrous semiconducting solid. Tellurium is also a semiconductor and is usually classified as a semimetal. Polonium, a radioactive element that occurs in trace amounts in uranium ores, is a silvery white metal. 

Dry photocopiers use an unusual property of selenium, the group 6A element below sulfur in the periodic table. Selenium is a photoconductor, a substance that is a poor electrical conductor when dark but whose conductivity increases (by a factor of 1000) when exposed to light. When the light is removed, the conductivity again drops. 

Identify the group 6A element that best fits each of the following descriptions ... 

Symbol of the Group 6A element that, like selenium, is a semiconductor. 

FIGURE 8.19 The Group 6A elements sulfur, selenium, and tellurium. Molecular axygen is a colorless, odorless gas. Polonium (not shown) is radioactive. 

Except for O, the Group 6A elements form a wide range of halides whose stability depends on crowding between lone pairs and surrounding halogen (X) atoms. Therefore, with increasing size of E and X, E—X bond length increases, electron repulsions between lone pairs and X atoms weaken. 

Phosphorus in Fertilizers 20.10 The Group 6A Elements The Chemistry of Oxygen The Chemistry of Sulfur Sulfur Oxides Oxyacids of Sulfur... 

Unlike the group 6A elements, all the halogens are typical nonmetals. Their melting and boiling points increase with increasing atomic number. Fluorine and chlorine are gases at room temperature, bromine is a liquid, and iodine is a solid. Each element consists of diatomic molecules E2, CI2, Br2, and I2 ( FIGURE 7.27). 

For the group 6A elements, what is the tiend in electronegativity with increasing atomic number ... 

Write the chemical formula for each of the following compounds, and indicate the oxidation state of the group 6A element in each (a) selenous acid, (b) potassium hydrogen sulfite, (c) hydrogen teUuride, (d) carbon disulfide, (e) calcium sulfate, (f) cadmium sulfide, (g) zinc teUuride. 

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