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METALS AND NONMETALS
There are some distinctions between 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. Their use in industry is
explained not only by those properties, but also by the fact that their properties,
such as strength and hardness, can be greatly improved by alloying them with other
metals.
There are several important groups of metals and alloys. The common metals such
as iron, copper, zinc, etc. are produced in great quantities.
The so-called precious metals include silver, gold, platinum and palladium. The
light metals are aluminum, beryllium and titanium. They are important in aircraft
and rocket construction.
Many elements are classified as semimetals (bismuth, for example) because they
have much poorer conductivity than common metals.
Nonmetals (carbon, silicon, sulphur) in the solid state are usually brittle materials
without metallic lustre and are usually poor conductors of electricity. Nonmetals
show greater variety of chemical properties than common metals do.
Metals can undergo corrosion, changing in this case their chemical and
electromechanical properties. In order to protect metals from corrosion the
products made of metals and steel are coated by some films (coatings). Organic
coatings protect metals and steel from corrosion by forming a corrosion-resistant
barrier between metal or steel and the corrosive environment.

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