sic definition centers around the type of bonding existing between the atoms of the element, and around the characteristics of certain of the electrons associated with these atoms. In a more practical way, however, a metal can be defined as an element which has a particular package of properties. Metals are crystalline when in the solid state and, with few exceptions ( . mercury), are solid at ambient temperatures. They are good conductors of heat and electricity and are opaque to light. They usually have a comparatively high density. Many metals are ductile-that is, their shape can be changed permanently by the application of a force without breaking. The forces required to cause this deformation and those required to break o r fracture a metal are comparatively high, although, the fracture forces is not nearly as high as would be expected f rom simple consideration of the forces required to tear apart the atoms of the metal. One of the more significant of these characteristics f rom our point of view is that of crystallinity. A crystalline solid is one in which the constituent atoms are located in a regular three-dimensional array as if they were located at the corners of the squares of a three-dimensional chessboard.
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