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VSEPR - Predicting the Shapes of Molecules

Looking first at simple molecules, where a central atom is surrounded by two or more other atoms,  there are only six unique electronic geometries that an organic chemist needs to be readily familiar with.  The electronic geometry is determined by how many bonding and non-bonding electron groups surround a central atom.

For each electronic geometry, there may be a number of different molecular geometries (the shape of a molecule when only bonded atoms are considered).  Representations are given below, manipulate the molecular geometries and see how they relate to the parent electronic geometry.

Though not important when determining the structure of most organic compounds, the trigonal bipyramidal and octahedral geometries are important when considering transition states during SN2 mechanisms or the geometry about transition metals in reagents or proteins.

Electronic Geometry
Molecular Geometries
 
Linear
BeH2
Linear
 
Trigonal planar
BF3
SO2
Trigonal planar
Bent
 
Tetrahedral
CH4
NH3
H2S
Tetrahedral
Trigonal pyramidal
Bent
 
Trigonal bipyramidal
PF5
TeCl4
BrF3
 XeF2
Trigonal bipyramidal
See-saw
T-shaped 
Linear
 
Octahedral
SF6
IF5
XeF4
Octahedral
Square pyramidal
Square planar


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© Dr. Ian Hunt, Department of Chemistry, University of Calgary