VSEPR Theory

There are ways to determine the shape any molecule has. The Valance Shell Electron Pair Repulsion Theory is one of the methods used to determine the shape of a compound. This exercise will allow you to build and view a few compounds to verify this theory.

1. Build and minimize methane, ammonia, and water. Record the energy and for each. (Hint: in PC Model you can convert methane to ammonia by changing the carbon to nitrogen, then use the Hadd function to give the appropriate number of hydrogens for the nitrogen). For each of these, use query to determine the center atom to hydrogen bond length and the angle indicated in the diagram below.
2. Do the bond lengths get smaller or larger going from methane to water?
3. What happens to the bond angles in each? What causes the change in bond angle?
4. What name is given to the shape of each compound?

Compound	Energy		Bond length	Bond angle	Name of Shape
methane
ammonia
water

Molecular structures of methane, ammonia, and water

Problem contributed by: Luise E. Strange (DeKalb College) Web implementation by: Luise E. Strange (DeKalb College)

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