Editing Octet rule (section)

===Low-dimensional geometries===
In the [[trigonal planar]] coordination geometry, one [[p orbital|''p'' orbital]] points out of the bonding plane, and can only [[orbital overlap|overlap]] with nearby atomic orbitals in a [[π bond]].  If that ''p'' orbital would be empty in an isolated atom, it may be filled through an intramolecular [[dative bond]], as with [[aminoboranes]].  However, in some cases (e.g. [[boron trichloride]] and various [[borane]]s, [[triphenylcarbenium|triphenylmethanium]]), no nearby filled orbital can profitably overlap with the empty ''p'' orbital.  In such cases, the orbital remains empty, and the compound obeys a "sextet rule".  Likewise, linear compounds, such as [[dimethylzinc]], have two ''p'' orbitals perpendicular to the bonding axis, and may obey a "quartet rule".<ref>{{cite book|pp=298-299|year=1985|publisher=Wiley|lccn=84-15310|isbn=0-471-87393-4|last1=Albright|first1=T.&nbsp;A.|last2=Burdett|first2=Jeremy&nbsp;K.|last3=Whangbo|first3=Myung-Hwan|title=Orbital Interactions in Chemistry}}</ref>  In either case, the empty unshielded orbitals tend to attract adducts.