Editing Crystal structure (section)

{{short description|Ordered arrangement of atoms, ions, or molecules in a crystalline material}}
[[File:Sodium-chloride-3D-ionic.png|thumb|Crystal structure of [[Sodium chloride|table salt]] (sodium in purple, chlorine in green)]]
In [[crystallography]], '''crystal structure''' is a description of ordered arrangement of [[atom]]s, [[ion]]s, or [[molecule]]s in a [[crystal|crystalline material]].<ref name="Solid State Physics 2010">{{cite book |title=Solid State Physics |edition=2nd |first1=J.R. |last1=Hook |first2=H.E. |last2=Hall |series=Manchester Physics Series |publisher=John Wiley & Sons |date=2010 |isbn=9780471928041 |url-access=registration |url=https://archive.org/details/solidstatephysic11cole_0 }}</ref> Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that repeat along the principal directions of [[Three-dimensional space (mathematics)|three-dimensional space]] in matter.

The smallest group of particles in a material that constitutes this repeating pattern is the [[unit cell]] of the structure. The unit cell completely reflects the symmetry and structure of the entire crystal, which is built up by repetitive [[Translation (geometry)|translation]] of the unit cell along its principal axes. The translation vectors define the nodes of the [[Bravais lattice]].

The lengths of principal axes/edges, of the unit cell and angles between them are [[lattice constant]]s, also called ''lattice parameters'' or ''cell parameters''. The [[symmetry]] properties of a crystal are described by the concept of [[space groups]].<ref name="Solid State Physics 2010"/> All possible symmetric arrangements of particles in three-dimensional space may be described by 230 space groups.

The crystal structure and symmetry play a critical role in determining many physical properties, such as [[cleavage (crystal)|cleavage]], [[electronic band structure]], and [[crystal optics|optical transparency]].