How are atoms arranged in a crystal

The Structure of crystals is through the two terms Grid and Base described.


The Crystal lattice, also Point grid called, is a three-dimensional arrangement of (mathematical) points. The smallest unit of the lattice is the unit cell. This contains all the information necessary to describe the crystal. These unit cells are expanded to a three-dimensional network by translational symmetry. The crystal lattice is a tool to describe the symmetry and geometry of a crystal. In three-dimensional space, the 14 Bravais grids describe every possibility of cell shape. From every lattice point of the cell the (infinitely extended) crystal must look exactly the same, no matter in which direction one looks. Because the crystal lattice is only made up of points, it is always centrosymmetric.

The primitive unit cell is a cell that contains only one grid point (it is shown darker in the graphic).



The Base a crystal structure are atoms, ions or molecules. These particles are arranged in the crystal lattice. The base consists of at least one atom, but it can also contain a few thousand atoms (protein crystals). In the case of sodium chloride, the base consists of a Na+- and a Cl-Ion.

The lattice structure is often used in the literature. One then speaks of Sodium chloride lattice, Cesium chloride lattice, etc. But because the crystal lattice contains only points and no ions, this expression is misleading. It says more precisely Sodium chloride structure, Cesium chloride structure, Diamond structure or Zinc blende structure. These structures are used for the typing of a number of other compounds, which correspond to the examples with regard to the crystal structure. So you can also use the terms Sodium chloride structure type, Cesium chloride structure type, etc. use.

See also


  • Arnold Fr. Holleman and Egon Wiberg: Inorganic Chemistry Textbook (101st edition), ISBN 3-11-012641-9

Categories: Crystallography | Crystal structure type | Chemical bond