Nonmetals elements Nonmetallic materials

The M-NM transition has been a topic of interest from the days of Sir Humphry Davy when sodium and potassium were discovered till then only high-density elements such as Au, Ag and Cu with lustre and other related properties were known to be metallic. A variety of materials exhibit a transition from the nonmetallic to the metallic state because of a change in crystal structure, composition, temperature or pressure. While the majority of elements in nature are metallic, some of the elements which are ordinarily nonmetals become metallic on application of pressure or on melting accordingly, silicon is metallic in the liquid state and nonmetallic in the solid state. Metals such as Cs and Hg become nonmetallic when expanded to low densities at high temperatures. Solutions of alkali metals in liquid ammonia become metallic when the concentration of the alkali metal is sufficiently high. Alkali metal tungsten bronzes... 

Materials that are poor conductors of electricity are generally considered nonmetals. One important use of nonmetals, in fact, is the capability to insulate against current flow. Earths atmosphere is composed of nonmetallic elements, but lightning can break down the electron bonds and allow huge voltages to make their way to the ground. Water in its pure form is nonmetallic, though it almost always contains impurities called electrolytes that allow for an electric field. 

An alloy is a metallic material that contains more than one element. Some alloys are simply solid solutions, while others are specific compounds with definite ratios of the component elements. Alloys have metallic properties, but they can consist of either two or more metals or a metal and a nonmetal. We broadly classify alloys as substitutional or interstitial, hi a substitutional alloy, one metal atom substitutes for another in the crystal stracture. The crystal structure may either stay the same upon the substitution, or it may change to accommodate the differences between the atoms. In an interstitial alloy, small, usually nonmetallic atoms fit in between the metallic atoms of a crystal. The alloy maintains its metallic properties with these interstitial atoms in the structure. 

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