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Not AvailableThe term "metal" designates an element which is good conductor of electricity and whose electric resistance is directly proportional to the absolute temperature (Wittmann, 1979). In addition to this distinctive characteristic, metals share several other typical physical properties such as high thermal conductivity, high density, malleability and ductility. Several non-metallic elements exhibit one or more of these properties, so that the only feature that defines a metal unambiguously is the electric conductivity which decreases with increasing temperature. Within a given period the properties of the elements vary gradually from a high electropositive (metallic) character at the left-hand side of the series to the highly electronegative (nonmetallic) character at the end of the series. The "metalloids" (or half metals) such as boron, silicon, germanium, arsenic and tellurium are balanced in the Periodic Table between metals and non-metalsNot Availabl