Editing Molecular geometry (section)

==Types of molecular structure==
A bond angle is the geometric angle between two adjacent bonds. Some common shapes of simple molecules include:
* '''[[Linear molecular geometry|Linear]]:''' In a linear model, atoms are connected in a straight line. The bond angles are set at 180°. For example, carbon dioxide and [[nitric oxide]] have a linear molecular shape.
* '''[[Trigonal planar molecular geometry|Trigonal planar]]:''' Molecules with the trigonal planar shape are somewhat triangular and in one [[Plane (geometry)|plane (flat)]].  Consequently, the bond angles are set at 120°. For example, [[boron trifluoride]].
* '''[[Bent molecular geometry|Angular]]:''' Angular molecules (also called ''bent'' or ''V-shaped'') have a non-linear shape. For example, water (H<sub>2</sub>O), which has an angle of about 105°. A water molecule has two pairs of bonded electrons and two unshared lone pairs.
* '''[[Tetrahedral molecular geometry|Tetrahedral]]:''' ''Tetra-'' signifies four, and ''-hedral'' relates to a face of a solid, so "[[tetrahedral]]" literally means "having four faces".  This shape is found when there are [[star (graph theory)|four bonds all on one central atom]], with no extra unshared [[electron]] pairs.  In accordance with the [[VSEPR]] (valence-shell electron pair repulsion theory), the bond angles between the electron bonds are [[Inverse trigonometric functions|arccos]](−{{sfrac|1|3}}) = 109.47°. For example, [[methane]] (CH<sub>4</sub>) is a tetrahedral molecule. <!-- what about molecules without a central atom, which form a complete graph? -->
* '''[[Octahedral molecular geometry|Octahedral]]:''' ''Octa-'' signifies eight, and ''-hedral'' relates to a face of a solid, so "[[octahedral]]" means "having eight faces". The bond angle is 90 degrees. For example, [[sulfur hexafluoride]] (SF<sub>6</sub>) is an octahedral molecule.
* '''[[Trigonal pyramidal molecular geometry|Trigonal pyramidal]]:''' A trigonal pyramidal molecule has a [[Pyramid (geometry)|pyramid-like shape]] with a triangular base.  Unlike the linear and trigonal planar shapes but similar to the tetrahedral orientation, pyramidal shapes require three dimensions in order to fully separate the electrons.  Here, there are only three pairs of bonded electrons, leaving one unshared lone pair. Lone pair – bond pair repulsions change the bond angle from the tetrahedral angle to a slightly lower value.<ref>Miessler G.L. and Tarr D.A. ''Inorganic Chemistry'' (2nd ed., Prentice-Hall 1999), pp.57-58</ref> For example, [[ammonia]] (NH<sub>3</sub>).

===VSEPR table===
{{main|VSEPR theory #AXE method}}
The bond angles in the table below are ideal angles from the simple [[VSEPR theory]] (pronounced "Vesper Theory"){{Citation needed|date=November 2021}}, followed by the actual angle for the example given in the following column where this differs. For many cases, such as trigonal pyramidal and bent, the actual angle for the example differs from the ideal angle, and examples differ by different amounts. For example, the angle in [[hydrogen sulfide|H<sub>2</sub>S]] (92°) differs from the tetrahedral angle by much more than the angle for [[water (molecule)|H<sub>2</sub>O]] (104.48°) does.
{| class="wikitable sortable" style="text-align: center;"
|-
! scope="col" | Atoms bonded to <br />central atom
! scope="col" | Lone pairs
! scope="col" | Electron domains <br />(Steric number)
! scope="col" | Shape
! scope="col" | Ideal bond angle <br />(example's bond angle)
! scope="col" | Example
! scope="col" | Image
|-
| 2
| 0
| 2
| style="text-align: left;" |  [[linear molecular geometry|linear]]
| 180°
| [[carbon dioxide|CO<sub>2</sub>]]
| [[Image:Linear-3D-balls.png|50px]]
|-
| 3
| 0
| 3
| style="text-align: left;" | [[trigonal planar molecular geometry|trigonal planar]]
| 120°
| [[Boron trifluoride|BF<sub>3</sub>]]
| [[Image:Trigonal-3D-balls.png|50px]]
|-
| 2
| 1
| 3
| style="text-align: left;" | [[Bent molecular geometry|bent]]
| 120° (119°) 
| [[Sulfur dioxide|SO<sub>2</sub>]]
| [[Image:Bent-3D-balls.png|50px]]
|-
| 4
| 0
| 4
| style="text-align: left;" | [[tetrahedral molecular geometry|tetrahedral]]
| 109.5°
| [[methane|CH<sub>4</sub>]]
| [[Image:AX4E0-3D-balls.png|50px]]
|-
| 3
| 1
| 4
| style="text-align: left;" | [[trigonal pyramidal molecular geometry|trigonal pyramidal]]
| 109.5° (106.8°)<ref name="CRC 94th">{{cite book | editor= Haynes, William M. | year = 2013 | title = CRC Handbook of Chemistry and Physics | edition = 94th | publisher = [[CRC Press]] | isbn = 9781466571143|pages=9–26| title-link = CRC Handbook of Chemistry and Physics }}</ref>
| [[ammonia|NH<sub>3</sub>]]
| [[Image:Pyramidal-3D-balls.png|50px]]
|-
| 2
| 2
| 4
| style="text-align: left;" | [[Bent molecular geometry|bent]]
| 109.5° (104.48°)<ref>{{cite journal|year=1979|last1=Hoy|first1=AR|last2=Bunker|first2=PR|journal=Journal of Molecular Spectroscopy|volume=74|pages=1–8|doi=10.1016/0022-2852(79)90019-5|title=A precise solution of the rotation bending Schrödinger equation for a triatomic molecule with application to the water molecule|issue=1|bibcode=1979JMoSp..74....1H}}</ref><ref>{{cite web |url=http://cccbdb.nist.gov/expangle2.asp?descript=aHOH&all=0 |title=CCCBDB Experimental bond angles page 2 |access-date=2014-08-27 |url-status=dead |archive-url=https://web.archive.org/web/20140903044129/http://cccbdb.nist.gov/expangle2.asp?descript=aHOH&all=0 |archive-date=2014-09-03 }}</ref> 
| [[H2O|H<sub>2</sub>O]]
| [[Image:Bent-3D-balls.png|50px]]
|-
| 5
| 0
| 5
| style="text-align: left;" | [[trigonal bipyramidal molecular geometry|trigonal bipyramidal]]
| 90°, 120° 
| [[phosphorus pentachloride|PCl<sub>5</sub>]]
| [[Image:Trigonal-bipyramidal-3D-balls.png|50px]]
|-
| 4
| 1
| 5
| style="text-align: left;" | [[seesaw molecular geometry|seesaw]]
| ax–ax 180° (173.1°), <br /> eq–eq 120° (101.6°), <br />ax–eq 90° 
| [[sulfur tetrafluoride|SF<sub>4</sub>]]
| [[Image:Seesaw-3D-balls.png|50px]]
|-
| 3
| 2
| 5
| style="text-align: left;" | [[T-shaped molecular geometry|T-shaped]]
| 90° (87.5°), 180° (175°) 
| [[chlorine trifluoride|ClF<sub>3</sub>]]
| [[Image:T-shaped-3D-balls.png|50px]]
|-
| 2
| 3
| 5
| style="text-align: left;" | [[linear molecular geometry|linear]]
| 180°
| [[xenon difluoride|XeF<sub>2</sub>]]
| [[Image:Linear-3D-balls.png|50px]]
|-
| 6
| 0
| 6
| style="text-align: left;" | [[octahedral molecular geometry|octahedral]]
| 90°, 180°
| [[sulfur hexafluoride|SF<sub>6</sub>]]
| [[Image:AX6E0-3D-balls.png|50px]]
|-
| 5
| 1
| 6
| style="text-align: left;" | [[square pyramidal molecular geometry|square pyramidal]]
| 90° (84.8°) 
| [[bromine pentafluoride|BrF<sub>5</sub>]]
| [[Image:Square-pyramidal-3D-balls.png|50px]]
|-
| 4
| 2
| 6
| style="text-align: left;" | [[square planar molecular geometry|square planar]]
| 90°, 180°
| [[xenon tetrafluoride|XeF<sub>4</sub>]]
| [[Image:Square-planar-3D-balls.png|50px]]
|-
| 7
| 0
| 7
| style="text-align: left;" | [[pentagonal bipyramidal molecular geometry|pentagonal bipyramidal]]
| 90°, 72°, 180°
| [[iodine heptafluoride|IF<sub>7</sub>]]
| [[Image:Pentagonal-bipyramidal-3D-balls.png|50px]]
|-
| 6
| 1
| 7
| style="text-align: left;" | [[pentagonal pyramidal molecular geometry|pentagonal pyramidal]]
| 72°, 90°, 144°
| {{chem2|XeOF5-}}
| [[Image:Pentagonal-pyramidal-3D-balls.png|50px]]
|-
| 5
| 2
| 7
| style="text-align: left;" | [[pentagonal planar molecular geometry|pentagonal planar]]
| 72°, 144°
| [[Tetramethylammonium pentafluoroxenate|{{chem2|XeF5-}}]]
| [[Image:Pentagonal-planar-3D-balls.png|50px]]
|-
| 8
| 0
| 8
| style="text-align: left;" | [[square antiprismatic molecular geometry|square antiprismatic]]
|
| [[Nitrosonium octafluoroxenate(VI)|{{chem2|XeF8(2-)}}]]
| [[Image:Square-antiprismatic-3D-balls.png|50px]]
|-
| 9
| 0
| 9
| style="text-align: left;" | [[tricapped trigonal prismatic molecular geometry|tricapped trigonal prismatic]]
|
| [[Potassium nonahydridorhenate|{{chem2|ReH9(2-)}}]]
| [[Image:AX9E0-3D-balls.png|50px]]
|}

The greater the number of lone pairs contained in a molecule, the smaller the angles between the atoms of that molecule. The [[VSEPR theory]] predicts that lone pairs repel each other, thus pushing the different atoms away from them.