Valence Shell Electron Pair Repulsion Theory

VSEPR Theory is one method that chemists use to predict the shapes of molecules. This theory predicts that electron pairs, whether involved in bonds or as non-bonding pairs, will adopt a geometry in which they maximize the distance from one another in order to minimize repulsions. This will result in a geometry with the lowest possible energy.

Two Regions of Electron Density

The maximum distance two regions of electron density can get away from affords a geometry called linear.

The red spheres represent the atoms in the molecule. The gray ovals represent bonding regions (a single bond, a double bond, or a triple bond - each represents one region).

Three Regions of Electron Density

The maximum distance three regions of electron density can get away from affords a geometry called trigonal planar.

There are two possible shapes of molecules whose geometry is trigonal planar. In the first instance, all the regions are bonding regions and the shape of the molecule is the same as the geometry around the central atom, trigonal planar. In the second instance, there are two bonding regions and one non-bonding region, the shape of molecules of this type is called bent.

The large gray areas represent non-bonding pairs of electrons.

Four Regions of Electron Density

The maximum distance four regions of electron density can get away from affords a geometry called tetrahedral.

There are three possible shapes of molecules whose geometry is tetrahedral. In the first instance, all the regions are bonding regions and the shape of the molecule is the same as the geometry around the central atom, tetrahedral. In the second instance, there are three bonding regions and one non-bonding region, the shape of molecules of this type is called trigonal pyramidal. In the third instance, there are two bonding regions and two non-bonding regions, the shape of molecules of this type is called bent.

Five Regions of Electron Density

The maximum distance five regions of electron density can get away from affords a geometry called trigonal bipyramidal.

There are four possible shapes of molecules whose geometry is trigonal bipyramidal. In the first instance, all the regions are bonding regions and the shape of the molecule is the same as the geometry around the central atom, trigonal bipyramidal. In the second instance, there are four bonding regions and one non-bonding region, the shape of molecules of this type is called distorted tetrahedral. In the third instance, there are three bonding regions and two non-bonding region, the shape of molecules of this type is called T-shaped. In the fourth instance, there are two bonding regions and three non-bonding regions, the shape of molecules of this type is called linear.

Six Regions of Electron Density

The maximum distance six regions of electron density can get away from affords a geometry called octahedral.

There are five possible shapes of molecules whose geometry is octahedral. In the first instance, all the regions are bonding regions and the shape of the molecule is the same as the geometry around the central atom, octahedral. In the second instance, there are five bonding regions and one non-bonding region, the shape of molecules of this type is called square pyramidal. In the third instance, there are four bonding regions and two non-bonding regions, the shape of molecules of this type is called square planar. In the fourth instance, there are three bonding regions and three non-bonding regions, the shape of molecules of this type is called T-shaped. In the fifth instance, there are four bonding regions and two non-bonding regions, the shape of molecules of this type is called linear.

1. Lewis Structures
2. Formal Charge
3. Resonance Structures
4. Valence Shell Electron Pair Repulsion Theory
5. Bond and Molecular Polarity
6. Intermolecular Forces
7. VSEPR Tutorial
8. VSEPR Quiz

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