Editing Structure (section)

== Chemical ==
{{Main|Chemical structure}}
[[File:Dopamin - Dopamine.svg|thumb|right|A skeletal formula for [[dopamine]]]]
Chemical structure refers to both molecular geometry and electronic structure. The structure can be represented by a variety of diagrams called [[structural formula]]s. [[Lewis structure]]s use a dot notation to represent the [[valence electron]]s for an atom; these are the electrons that determine the role of the atom in chemical reactions.<ref>{{cite book|last1=DeKock|first1=Roger L.|last2=Gray|first2=Harry B.|title=Chemical structure and bonding|date=1989|publisher=University Science Books|location=Mill Valley, Calif.|isbn=9780935702613|edition=2nd|url-access=registration|url=https://archive.org/details/isbn_9780935702613}}</ref>{{rp|71–72}} Bonds between atoms can be represented by lines with one line for each pair of electrons that is shared. In a simplified version of such a diagram, called a [[skeletal formula]], only carbon-carbon bonds and functional groups are shown.<ref>{{cite book|last1=Hill|first1=Graham C.|last2=Holman|first2=John S.|title=Chemistry in context|date=2000|publisher=Nelson|location=Walton-on-Thames|isbn=9780174482765|page=391|edition=5th}}</ref>

Atoms in a crystal have a [[crystal structure|structure]] that involves repetition of a basic unit called a ''unit cell''. The atoms can be modeled as points on a [[Bravais lattice|lattice]], and one can explore the effect of [[symmetry]] operations that include rotations about a point, reflections about a symmetry planes, and ''[[translation (geometry)|translations]]'' (movements of all the points by the same amount). Each crystal has a finite group, called the [[space group]], of such operations that map it onto itself; there are 230 possible space groups.<ref name=Ashcroft>{{cite book|last1=Ashcroft|first1=Neil W.|last2=Mermin|first2=N. David|title=Solid state physics|date=1977|publisher=Holt, Rinehart and Winston|location=New York|isbn=9780030839931|edition=27. repr.|url-access=registration|url=https://archive.org/details/solidstatephysic00ashc}}</ref>{{rp|125–126}} By [[Neumann's law]], the symmetry of a crystal determines what physical properties, including [[piezoelectricity]] and [[ferromagnetism]], the crystal can have.<ref>{{cite book|last1=Newnham|first1=Robert E.|title=Properties of materials anisotropy, symmetry, structure|date=2005|publisher=Oxford University Press|location=Oxford|isbn=9780191523403}}</ref>{{rp|34–36,91–92,168–169}}