VSEPR theory

VSEPR theory (Valence Shell Electron Pair Repulsion theory) is a model used in chemistry to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms. The theory is based on the idea that electron pairs around a central atom will arrange themselves as far apart as possible to minimize repulsion.

History

The VSEPR model was first proposed by Ronald Gillespie and Ronald Nyholm in 1957. It was developed to explain the shapes of molecules and ions that could not be described by the Lewis structure model alone.

Basic Principles

The VSEPR theory is based on the following principles:

• Electron pairs, both bonding and non-bonding, repel each other.
• The shape of a molecule is determined by the number of electron pairs around the central atom.
• Lone pairs occupy more space than bonding pairs, leading to distortions in molecular geometry.

Molecular Geometries

The VSEPR model predicts several common molecular geometries:

Linear

Molecules with two electron pairs around the central atom adopt a linear geometry. An example is carbon dioxide (CO_).

Trigonal Planar

Three electron pairs around the central atom result in a trigonal planar shape, as seen in boron trifluoride (BF_).

Tetrahedral

Four electron pairs form a tetrahedral shape, exemplified by methane (CH_).

Trigonal Bipyramidal

Five electron pairs lead to a trigonal bipyramidal geometry, such as in phosphorus pentachloride (PCl_).

Octahedral

Six electron pairs result in an octahedral shape, as seen in sulfur hexafluoride (SF_).

Effect of Lone Pairs

Lone pairs of electrons occupy more space than bonding pairs, causing deviations from ideal geometries. For example, in water (H_O), the two lone pairs on oxygen result in a bent shape rather than a linear one.

Applications

VSEPR theory is widely used in inorganic chemistry and organic chemistry to predict the shapes of molecules and ions. It is particularly useful for understanding the geometry of transition metal complexes.

Limitations

While VSEPR theory is useful for predicting molecular shapes, it does not account for the effects of electronegativity or the presence of multiple bonds. It also does not explain the relative strengths of different types of repulsions.

Related pages

• Molecular geometry
• Chemical bonding
• Lewis structure

References

• Gillespie, R. J., & Nyholm, R. S. (1957). Inorganic stereochemistry. Quarterly Reviews, Chemical Society, 11(3), 339-380.
• Greenwood, N. N., & Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann.

Gallery

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  Water molecule dimensions
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  Sulfur tetrafluoride dimensions
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  Linear geometry
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  Trigonal planar geometry
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  Bent geometry
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  Tetrahedral geometry
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  Trigonal pyramidal geometry
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  Bent geometry
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  Trigonal bipyramidal geometry
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  Seesaw geometry
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  T-shaped geometry
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  Linear geometry
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  Octahedral geometry
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  Square pyramidal geometry
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  Square planar geometry
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  Pentagonal bipyramidal geometry
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  Pentagonal pyramidal geometry
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  Pentagonal planar geometry
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  Linear 3D model
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  Bent 3D model
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  Linear 3D model
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  Linear 3D model
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  Trigonal planar 3D model
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  Trigonal pyramidal 3D model
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  T-shaped 3D model
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  T-shaped 3D model
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  Tetrahedral 3D model
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  Seesaw 3D model
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  Square planar 3D model
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  Trigonal bipyramidal 3D model
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  Trigonal bipyramidal 3D model
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  Square pyramidal 3D model
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  Pentagonal planar 3D model
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  Pentagonal planar 3D model
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  Octahedral 3D model
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  Octahedral 3D model
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  Pentagonal pyramidal 3D model
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  Pentagonal pyramidal 3D model
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  Pentagonal bipyramidal 3D model
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  Pentagonal bipyramidal 3D model
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  Square antiprismatic 3D model
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  Square antiprismatic 3D model
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  Linear 3D model
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  Trigonal 3D model
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  Tetrahedral 3D model
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  Trigonal bipyramidal 3D model
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  Square pyramidal 3D model
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  Octahedral 3D model
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  Pentagonal bipyramidal 3D model
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  Face-capped octahedron
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  Monocapped trigonal prism
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  Square antiprismatic 3D model
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  Snub disphenoid
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  Square face bicapped trigonal prism
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  3D model
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  Monocapped square antiprism
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  Xenon hexafluoride
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  Hexamethyl tungsten
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  Bent 3D model
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  Pyramidal 3D model
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  Tetrahedral 3D model
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  Square pyramidal 3D model
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  Prismatic trigonal prism

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