Most of the elements, as well as most inorganic compounds, exist as solids. The ideas
about symmetry point groups can be applied to molecules or ions in crystal lattices in the context
of site symmetry and pseudosymmetry. A crystal results from the periodic repetition of a
specific arrangement of atoms through space. For a regular infinite array of objects the act of
translation in space can be a valid symmetry operation, in addition to those described previously.
Consider the infinite one-dimensional lattice