Properties of selena and tellura\n08.02.2017\n\n\n\nThe tellur element was discovered by the claprote in 1782 in Hungarian gold-bearing ores. The name tellur comes from the Greek \"tellus\" - earth. In 1817, bercellus discovered in the sludge of the sulfuric acid plant an element close to tellur. It was named after the Greek name of the moon, selenom. Selenium and tellur are elements of the sixth group of the periodic system. They are chemically close to sulphur, but differ from it, in particular tellurium, by distinct metal properties. Like the sulfur of nets and tellurium break out amorphous and crystalline forms. Two crystalline modifications of selenium are known. It is the most resistant grey or metal selenium with hexagonal structure (a = 4.354 a, c = 4.949 a). When precipitation of selenium from solutions or rapid cooling of selenium vapour is produced as a loose red powder, the red selenium has a monocline crystalline structure. When heated to 120 degrees, the red selenium turns grey. Glass-shaped selenium is produced when the melted selenium is rapidly cooled in the form of a fragile sero-lead mass. At a temperature of about 50 degrees glass selenium begins to soften, at a higher temperature it passes into crystalline grey selenium. Crystalline tellurium is produced by condensing tellurium vapour. It has a silver white color. Two modifications of tellurium are known - a-and b-tellurium, hexagonal modification of isomorphine to seroma selena (a = 4,445 a, c = 5.91 a). From aqueous solutions, reagents deposit brown powder amorphous tellurium. The physical properties of selena and telluraselen are typical semiconductors. At room temperature, he's not good at electrical current. The electrical conductivity of selenium depends heavily on the intensity of lighting. Electricity conductivity is 1,000 times higher in the light than in the dark. The greatest effect is caused by rays with a wavelength of about 700 ml. Tellur has a higher electrical conductivity than selenium, and electrical resistance increases significantly at high pressures. Both elements are fragile at normal temperature, but are susceptible to plastic deformation when heated. Selenium and tellurium do not react with oxygen at normal temperature. When heated in the air, they are oxidized with ignition to form seo2 and teo2. Selenium burns with a blue flame, tellur - with a blue flame with a greenish kayemaking. Burning selenium is accompanied by a characteristic smell (\" smell of rotten radish \"). Water and non-oxidizing acids (diluted sulphuric acid and hydrochloric acid) do not affect selenium and tellurium. Elements are dissolved in concentrated sulfuric acid, nitric acid, and hot concentrated alkaline solutions. An important characteristic of selenium and tellurium, which are used in the technology of their production, is their ability to dissolve in sulfur alkali with the formation of polysulphides, which are easily degradable by acids with the release of selenium and tellurium, respectively. Selenium is dissolved in sodium sulphide solutions to form a compound of the type of thiosulphate na2seso3, which decomposes when acidified, releasing elemental selenium. Co all halogens selenium and tellurium react at normal temperature. With metals, they form selenides and tellurides similar to sulphides (e.g. Na2se, ag2se, etc.). Like sulphur, selenium and telluride form gaseous selenoid (h2se) and telluride (h2te) produced by the action of acids on selenides and tellurides. The elemental tellur is not directly connected to hydrogen, and selenium reacts with hydrogen at a rate above 400 degrees.\n\n\n\n\n\nContact facebookclassmate mirtwitterlivejournalprocessing Germanic waste
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