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02.04.2021 10:02

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Поставить предложения в вопросительную и отрицательную форму. c. he is still sitting near the fire. переведите текст metals, group of chemical elements that exhibit all or most of the following physical qualities: they are solid at ordinary temperatures; opaque; except in extremely thin films; good electrical and thermal conductors; lustrous when polished; and have a crystalline structure when in the solid state. metals and nonmetals are separated in the periodic table by a diagonal line of elements. elements to the left of this diagonal are metals, and elements to the right are nonmetals. elements that make up this diagonal—boron, silicon, germanium, arsenic, antimony, tellurium, polonium, and astatine—have both metallic and nonmetallic properties. the common metallic elements include the following: aluminum, barium, beryllium, bismuth, cadmium, calcium, cerium, chromium, cobalt, copper, gold, iridium, iron, lead, lithium, magnesium, manganese, mercury, molybdenum, nickel, osmium, palladium, platinum, potassium, radium, rhodium, silver, sodium, tantalum, thallium, thorium, tin, titanium, tungsten, uranium, vanadium, and zinc. metallic elements can combine with one another and with certain other elements, either as compounds, as solutions, or as intimate mixtures. a substance composed of two or more metals, or a substance composed of a metal and certain nonmetals such as carbon are called alloys. alloys of mercury with other metallic elements are known as amalgams. within the general limits of the definition of a metal, the properties of metals vary widely. most metals are grayish in color, but bismuth is pinkish, copper is red, and gold is yellow. some metals display more than one colour, a phenomenon called pleochroism. the melting points of metals range from about -39° c (about -38° f) for mercury to 3410° c (6170° f) for tungsten. osmium and iridium (specific gravity 22.6) are the densest metals, and lithium (specific gravity 0.53) is the least dense. the majority of metals crystallize in the cubic system, but some crystallize in the hexagonal and tetragonal systems (see crystal). bismuth has the lowest electrical conductivity of the metallic elements, and silvers the highest at ordinary temperatures. the conductivity of most metals can be lowered by alloying. all metals expand when heated and contract when cooled, but certain alloys, such as platinum and iridium alloys, have extremely low coefficients of expansion.