Editing VSEPR theory (section)

==Examples==
The [[methane]] molecule (CH<sub>4</sub>) is tetrahedral because there are four pairs of electrons. The four hydrogen atoms are positioned at the vertices of a [[tetrahedron]], and the bond angle is [[Inverse trigonometric functions|cos<sup>−1</sup>]](−{{frac|1|3}})&nbsp;≈&nbsp;109°&nbsp;28′.<ref>{{cite journal | last1 = Brittin | first1 = W. E. | year = 1945 | title = Valence Angle of the Tetrahedral Carbon Atom | journal = J. Chem. Educ. | volume = 22 | issue = 3| page = 145 | doi=10.1021/ed022p145| bibcode = 1945JChEd..22..145B }}</ref><ref>[http://maze5.net/?page_id=367 "Angle Between 2 Legs of a Tetrahedron"] {{Webarchive|url=https://web.archive.org/web/20181003122307/http://maze5.net/?page_id=367 |date=2018-10-03 }} – Maze5.net</ref> This is referred to as an AX<sub>4</sub> type of molecule. As mentioned above, A represents the central atom and X represents an outer atom.<ref name=Petrucci/>{{rp|410–417}}

The [[ammonia]] molecule (NH<sub>3</sub>) has three pairs of electrons involved in bonding, but there is a lone pair of electrons on the nitrogen atom.<ref name=Petrucci/>{{rp|392–393}} It is not bonded with another atom; however, it influences the overall shape through repulsions. As in methane above, there are four regions of electron density. Therefore, the overall orientation of the regions of electron density is tetrahedral. On the other hand, there are only three outer atoms. This is referred to as an AX<sub>3</sub>E type molecule because the lone pair is represented by an E.<ref name=Petrucci/>{{rp|410–417}} By definition, the molecular shape or geometry describes the geometric arrangement of the atomic nuclei only, which is trigonal-pyramidal for NH<sub>3</sub>.<ref name=Petrucci/>{{rp|410–417}}

Steric numbers of 7 or greater are possible, but are less common. The steric number of 7 occurs in [[iodine heptafluoride]] (IF<sub>7</sub>); the base geometry for a steric number of 7 is pentagonal bipyramidal.<ref name=Miessler/> The most common geometry for a steric number of 8 is a [[square antiprism]]atic geometry.<ref name="wiberg">{{cite book| first1 = E.| last1 = Wiberg| first2 = A. F.|last2= Holleman| title = Inorganic Chemistry| publisher = Academic Press| year = 2001| isbn = 978-0-12-352651-9}}</ref>{{rp|1165}} Examples of this include the octacyanomolybdate ({{chem|Mo(CN)|8|4-}}) and octafluorozirconate ({{chem|ZrF|8|4-}}) anions.<ref name="wiberg" />{{rp|1165}} The nonahydridorhenate ion ({{chem|ReH|9|2-}}) in [[potassium nonahydridorhenate]] is a rare example of a compound with a steric number of 9, which has a tricapped trigonal prismatic geometry.<ref name=Housecroft>{{cite book|last1=Housecroft |first1=C. E. |last2=Sharpe |first2=A. G. |title=Inorganic Chemistry|edition=2nd |publisher=Pearson |date=2005 |isbn=978-0-130-39913-7}}</ref>{{rp|254}}<ref name="wiberg" />

Steric numbers beyond 9 are very rare, and it is not clear what geometry is generally favoured.<ref>{{cite book |last=Wulfsberg |first=Gary |author-link= |date=2000 |title=Inorganic Chemistry |url= |location= |publisher=University Science Books |page=107 |isbn=9781891389016}}</ref> Possible geometries for steric numbers of 10, 11, 12, or 14 are [[gyroelongated square bipyramid|bicapped square antiprismatic]] (or bicapped [[dodecadeltahedral]]), [[edge-contracted icosahedron|octadecahedral]], [[regular icosahedron|icosahedral]], and bicapped [[hexagonal antiprism]]atic, respectively. No compounds with steric numbers this high involving [[denticity|monodentate]] ligands exist, and those involving multidentate ligands can often be analysed more simply as complexes with lower steric numbers when some multidentate ligands are treated as a unit.<ref name="wiberg" />{{rp|1165,1721}}