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Molecular Geometry
Chemistry Materials from Ray Tedder

Using VSEPR (valence shell electron pair repulsion) theory to predict molecular shapes.

One of the most difficult things that high school chemistry students are asked to do is to predict the shapes of molecules.  For most students, this process asks them to think in ways that they've never been asked to do it before.  It asks them to convert a 2-dimensional shape into a 3-dimensional shape.  This graphic will help students to predict shapes accurately until they can "see" these 3-dimensional shapes in their mind.  
As the instructions below tell you, you must start with a Lewis structure.  Once you have drawn the correct Lewis structure, select the structure below that has the correct number of electron pairs (both shared electron pairs and lone pairs) around the central atom in the Lewis structure. You can then draw the modified electron pair shape and finally the molecular shape. 
By following this process it is possible for students to see why the resulting molecular shape has the name that is has and to see how the unbonded elecron pairs (lone pairs) can force the molecule into the shapes that it adopts.    

The step-by-step process.
Figure 1. This illustration shows how to start with Lewis structure and walk through the steps.





Refer to Chemistry Matter and Change, Glencoe, 2002, pages 259-262 for an explanation of molecular shapes.