Q. Define the crystal symmetry with reference to crystal structure.
Ans.CRYSTAL SYMMETRY: A crystal is an orderly array of atoms in space. Atoms organize themselves in an orderly, three-dimensional symmetrical patterns , in that rows can be identified running in various directions along which the atoms are regularly spaced .the lo9cation of the atoms and their particular arrangement in a given crystal are described by means of a space lattice, which is a three dimensional network to straight lines that acts as a coordinate system in space.thi8s shows the internal symmetry of a crystal because a definite pattern is repeated over and over again a\indefinite directions in the space. The external symmetry of a crystal corresponds with the internal symmetry of the crystal. The most important elements of external symmetry of a crystal are (a) A centre (b) An axis and (c) A plane.
A centre of symmetry is a point in the crystal such that any straight line through it, person through a pair of similar point situated at the same distance but on opposite sides of the center of symmetry.