VSEPR electron Group Distribution

Procedure for applying VSEPR to determine molecular shape:

• Draw Lewis structure for species
• Count number of electron groups around central atom(s)
Any of the following qualifies as ONE electron group:
• single bond
• double bond
• triple bond
• lone pair
• single electron
• Use following table to determine spatial distribution of electron groups
• Based on number of electron groups used to bond terminal atoms, use following table to determine molecular shape

• The Lewis structure(s) (including resonance forms) are




• The number of electron groups around the central P atom is 3 (this is true in any of the resonance forms)
• The distribution of electron groups is trigonal planar
• All electron groups bond terminal atoms. Therefore the molecular shape is also trigonal planar.

# Electron Groups	Group Distribution	Stereochemistry	Visual Description	Examples
2	linear		linear	BeH2 (gas)
3	trigonal planar		trigonal planar       bent	BCl3, COCl2       SnCl2, SO2, NOCl
4	tetrahedral		tetrahedral       trigonal pyramidal       bent	CH4, POCl3, SO2Cl2     NH3, SO32-, SOCl2     H2O, ClO2-
5	trigonal bipyramidal Note: LP go in equatorial position because they repel less here.  Similarly, least electronegative groups go equatorial		trigonal bipyramidal 120o, 90o       see-saw <120o, <90o       T <90o       linear 180o	PF5         SF4, IO2F2-         BrF3         XeF2
6	octahedral		octahedral, 90o         square pyramid, 90o         square planar, 90o	SF6         BrF5         IF4-