Group Oxygen Selenium Sulfur

Basic physical properties of sulfur, selenium, and tellurium are indicated in Table 1.3. Downward the sulfur sub-group, the metallic character increases from sulfur to polonium, so that whereas there exist various non-metallic allotropic states of elementary sulfur, only one allotropic form of selenium is (semi)metallic, and the (semi)metallic form of tellurium is the most common for this element. Polonium is a typical metal. Physically, this trend is reflected in the electrical properties of the elements oxygen and sulfur are insulators, selenium and tellurium behave as semiconductors, and polonium is a typical metallic conductor. The temperature coefficient of resistivity for S, Se, and Te is negative, which is usually considered... 

Among the oxygen group elements, while sulfur is oxidized to +6 oxidation state (in H2SO4), selenium and tellurium are oxidized to +4 oxyacids with the liberation of nitrogen dioxide ... 

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. 

The poor metals among the BCNOs usually include aluminum, gallium, indium, thallium, tin, lead, and bismuth. The metalloids are boron, silicon, germanium, arsenic, antimony, tellurium, and polonium. The nonmetals are carbon, nitrogen, oxygen, phosphorus, sulfur and selenium. These groups are not official, and chemists sometimes disagree on whether a particular element like boron should be called a metal or a metalloid. 

Oxygen has been used as an example of an exocylic substituent in heterocycles (7)—(12) but other groups such as imine, thiocarbonyl, and substituted methylene are common. The majority of 6-6 heterocycles are associated with nitrogen, oxygen, and sulfur as heteroatoms other heteroatoms such as selenium and phosphorus are less common. 

Group VI, the oxygen. group Oxygen and its congeners sulfur and selenium are non-metals, whereas tellurium and polonium are classed as metalloids. The chemistry of oxygen is discussed in Chapter 6, and that of sulfur and its congeners in Chapter 17. 

Sulfur belongs to the chalcogen family. Other members of the family are oxygen, selenium, tellurium, and polonium. These elements make up Group 16 (VIA) of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. 

Polonium is the most metallic member of group 6A. But it is not a typical metal. It is rare, radioactive, and extremely toxic. Polonium is important historically because it was discovered by Marie and Pierre Curie in 1898 and named for Marie s nabve land, Poland. Selenium and tellurium are metalloids oxygen and sulfur are nonmetals. There are some trends to note in group 6A. With six valence electrons, the elements act mainly as nonmetals. They tend to gain two electrons to form ions with a 2— charge they also can share two electrons to achieve a stable electron configuration. 

Each Group VIA element is less electronegative than its neighboring halogen. Oxygen and sulfur are clearly nonmetallic, but selenium is less so. Tellurium is usually classified as a metalloid and forms metal-like crystals. Its chemistry is mostly that of a nonmetal. Polonium is a metal. All 29 isotopes of polonium are radioactive. 

The pATa of isoselenazoles was measured by spectrophotometric methods. The values were compared to isothiazoles and isoxazoles (Table 8). The basicity increases from oxygen to sulfur to selenium, being enhanced by the dimethyl groups <88H(27)243i>. 

The trend from nonmetalfic to metallic character upon going down the group is exemphfied by the conductivities of these elements. Sulfur is an insulator, selenium and tellurium are semiconductors, while the conductivity of polonium is typical of a true metal. In addition, the conductivities of sulfur, selenium, and tellurium increase with increasing temperature, behavior typical of nonmetals, whereas that of polonium increases at lower temperatures, typical of metals, see also Arsenic Boron Carbon Fullerenes Oxygen Ozone Phosphorus Selenium Sulfur Tin. 

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