Among the more obvious distinctions between different kinds of elements is that which divides metals and nonmetals. Metals are distinguished from nonmetals by their high conductivity for heat and electricity, by metallic lustre and by their resistance to electric current increasing with increasing temperature. Their widespread use in industry is due not only to those properties, but also to the fact that their properties can be greatly altered by alloying with other metals, so as to increase their strength or improve other properties such as hardness, etc.
There are several important groupings of metals and of the alloys of which they are the major constituents. The common metals such as iron, copper, zinc, lead, etc., are produced in great quantities. The so-called precious metals include silver, gold, platinum, palladium, and indium. The light metals are aluminium, berillium, magnesium and titanium. They are especially important in aircraft and rocket construction. The noble metals are most resistant to high temperature oxidation. Contrasting with these are the chemically reactive base metals. The alkali metals such as lithium, sodium, potassium are soft, low melting and rapidly oxidizing. The alkali earth metals such as calcium, strontium and radium are employed principally in the form of compounds. The rare-earth metals are the elements such as cerium and lutetium. There is a group of transition metals such as scandium, nickel, palladium and some others. The refractory metals, possessing high melting points, have received increasing attention of late in connection with their use in turbines, jet and highspeed aircraft. They are such metals as tungsten, molybdenum, tantalum, niobium. Tungsten has a melting point of 3 387° С. At the other extreme the low melting metals (rubidium, cesium, mercury) melt just above room temperature, and mercury melts at – 8.87° С. Many elements are classed as semimetals (arsenic, antimony and bismuth, for example) because they possess much poorer conductivities than the true metals and may be classed with the semiconductors, which differ from metals in that their conductivity increases with increasing temperature.
Nonmetals in the; solid state are usually brittle materials without metallic lustre and are usually poor conductors of heat and electricity. In some other physical properties non-metals have extreme range in melting point from helium (– 269°C) to carbon (above 3 500° С), and in hardness from diamond to soft white phosphorus. Nonmetals show an even greater variety of chemical properties than do the metals. Some (argon, helium, neon) form no compounds at all, while others (chlorine, fluorine) are highly active. Metals far out number the nonmetals, only 20 of all the known elements being considered definitely nonmetals.
Дополнительные слова и словосочетания:
1) differ from – различаться, отличаться от
2) increasing temperature – возрастающая температура
3) possess, v – обладать, владеть
4) widespread use – широко распространенное
использование
IX. Прочтите текст и дайте краткое содержание текста в 4-x предложениях.
X. Укажите предложения, которые соответствуют содержанию текста.
1. The noble metals are most resistant to refining oxidation.
2. Metals are distinguished from nonmetals by their high conductivity for heat and electricity.
3. Nonmetals in the solid state are usually refractory materials without metallic lustre and are usually solid at room temperature.
4. The alkali metals are soft, low melting and rapidly oxidizing and have small grain structure.
5. The rare-earth metals are the elements such as cerium and lutetium.
6. The common metals are produced in great quantities by the acid open-hearth process.
XI. Вставьте нужные по смыслу слова.
1. Metals are … from nonmetals by their high … for heat and electricity, by metallic … and by their resistance to … increasing with increasing …
a) vary greatly; elasticity; metal fatigue; corrosion; number of grains;
b) distinguished; conductivity; lustre; electric current; temperature;
c) differ; purity; grain structure; open-hearth processes; temperature of melting.
2. The … metals, possessing high …, have received increasing attention of late in connection with their use in turbines, jet and highspeed aircraft.
a) alkali; outstanding properties;
b) high-quality; tensile strength;
c) refractory; melting points.
3. There are several important groupings of … and of the alloys of which they are the major …
a) metals; constituents;
b) properties; producers;
c) stiffness; melting capacity.
XII. Определите, о каких из перечисленных ниже фактах можно узнать из текста.
1. Сталь более пластичная и ковкая по-сравнению с литейным чугуном.
2. Используя таблицу Менделеева можно предсказывать свойства неизвестных элементов.
3. Металлы отличаются от неметаллов тем, что обладают высокой тепло и электропроводностью, металлическим блеском и сопротивлением электрическому току, которое возрастает с увеличением температуры.
4. Чушковый чугун, стальной лом и другие материалы загружаются в печь через завалочное окно.
5. Неметаллы обнаруживают гораздо большее разнообразие химических свойств по-сравнению с металлами.
XIII. Закончите следующие предложения в соответствии с содержанием текста.
1. Metals far out number the nonmetals, only 20 of all the known elements …
а) likely increase in future;
b) may be derived from crystal-structure data;
с) being considered definitely nonmetals.
2. The alkali earth metals such as calcium, strontium and radium are employed principally …
a) with certain desired properties;
b) in the form of compounds;
c) the rate of oxidation becomes slow.
3. Many elements are classed as semimetals because they possess much poorer conductivities than the true metals and may be classed with the semiconductors, which differ from metals in that …
a) the number of electrons required to complete a shell;
b) the crystalline substances are composed of are arranged in regular order;
c) their conductivity increases with increasing temperature.
XIV. Выберите из текста предложения в которых даны характеристики различных групп металлов.
XV. Составьте план к тексту на русском языке.