Lewis structures may give us insight into how electrons might be shared in covalent bonding but they fail in one very important aspect of understanding molecular structure: most molecules are not "flat".

At first thought this may seem a minor problem. But because bonding electrons are usually not shared equally except in the simplest molecules , the overall shape of a molecule will in turn determine whether there is a symmetrical distribution of electron charge (i.e., negative charge) around a molecule. And as we will see later, that issue affects a host of chemical and physical behaviors.

So how does one get from a two-dimensional Lewis diagram to a three-dimensional picture of molecular structure?

One of the early proposals to explain the geometries of molecules was proposed by Linus Pauling. His main idea, that in molecules the atomic orbitals we have studied "hybridize" into new orbitals with specific shapes, is something we will look at a little later.