المواد الهندسية الجزء الاول

Orderliness in the arrangement of atoms and molecules in solids and liquids. Orderliness overdistances comparable to interatomic distances is called short-range order, whereas orderlinessrepeated over infinitely great distances is called longrange order. In an ideal gas the arrangementof an atom at any point in space is independent of the arrangement of other atoms. Thus, bothlong-range and short-range order are absent in the ideal gas, but liquids and amorphous solidsexhibit short-rangeordera certain regularity in the arrangement of the neighboring atoms. At greatdistances the order becomes “blurred” and gradually gives way to “disorder.” which means that long-range order does not exist in liquids and amorphous solids.
In crystals, the atoms are arranged in regular rows or networks (in three-dimensional lattices), and aregular alternation of atoms separated by the same distances is repeated for atoms separated byany distance—that is, both long-range and short-range order exist. The basic criteria of long-rangeorder are the symmetry and regularity of arrangement of particles, which repeat at any distancefrom a given atom.