tin (redirected from Tin compounds)

tin, metallic chemical element; symbol Sn [Lat. stannum]; at. no. 50; at. wt. 118.69; m.p. 231.9681°C;; b.p. 2,270°C;; sp. gr. 5.75 (gray), 7.3 (white); valence +2 or +4. Tin exhibits allotropy; above 13.2°C; it is a lustrous, silver-white, highly crystalline metal with tetragonal structure. A brittle form with orthorhombic structure may exist above 161°C;. Below 13.2°C; pure tin tends to become a gray powder, a change commonly designated "tin pest" or "tin disease." Tin is very soft (only slightly harder than lead) and malleable; it can be rolled, pressed, or hammered into extremely thin sheets (tin foil). When iron or steel is dipped into molten tin, a layer of tin is deposited on the surface. A tin coating may also be applied by electroplating, which uses less tin. The tin serves to prevent rusting, since it is barely affected by moisture. The tin plate used in tin cans is an iron or steel sheet coated with tin. A tin coating is used to protect copper and other metals. Tin is a component of antifriction metal, bell metal, britannia metal, bronze, gunmetal, pewter, solder, and other alloys. Tin forms stannous compounds, in which it has valence +2, and stannic compounds, in which it has valence +4, as well as stannites, stannates, and other complex salts. Industrially useful compounds of tin include stannous chloride, important as a reducing agent, as a mordant in dyeing, and for weighting silk; stannic chloride, for the last two purposes and to stabilize perfume and color in soap; stannic oxide, for the preparation of white porcelain enamelware; and sodium stannite, a reducing agent. Stannous fluoride is added to toothpastes and water supplies to prevent tooth decay. Tin forms a number of toxic organometallic compounds that are used as fungicides, catalysts, and for other uses. Tin very rarely occurs uncombined in nature; the dioxide, which occurs as cassiterite, or tinstone, is the only ore of commercial importance. It is obtained chiefly from Bolivia, Indonesia, the Malay Peninsula, Congo (Kinshasa), and Nigeria. The tin mines of Cornwall, England, were formerly the principal source. The metal is prepared from cassiterite by heating in the reverberatory furnace. The ore from the mines is first given special treatment, and the "concentrates" thus obtained are mixed with coal in the furnaces. Tin was known and used by humans at least as early as the Bronze Age. The metal and its compounds were known and used by the alchemists. In 1673, Robert Boyle published a description of experiments on the oxidation (calcination) of tin. The metal was recognized as an element by Lavoisier.

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tin

Metallic chemical element, chemical symbol Sn, atomic number 50. It is a soft, silvery white metal with a bluish tinge, employed since antiquity in the traditional form of bronze, its alloy with copper. It occurs chiefly as the dioxide (stannic oxide, SnO₂) in cassiterite. Since it is nontoxic, ductile, malleable, and easily worked, it is used to plate steel cans (“tin cans”) for use as food containers and to coat and plate other items. Pure tin is too weak to be used alone, but its many alloys include soft solder, pewter, bronze, and low-temperature casting alloys. It has valence 2 or 4 in compounds, including stannous chloride (used in tin galvanizing and manufacturing polymers and dyes), stannous oxide (used to make tin salts for chemical reagents and plating), stannous fluoride (used as an anticavity ingredient in toothpastes), stannic chloride (a stabilizer for perfumes and a source of other tin salts), and stannic oxide (a catalyst and a polishing powder for steel). Tin bonds with carbon to form organotin compounds, used to stabilize PVC and in biocides and fungicides.

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