In the last section we learned about a simple approach called
the Lewis-Dot structure that gives a good approximation of how
the valence electrons are distributed in a molecule. What Lewis-
Dot strucutres do not tell us is the shape of the molecule. For
example, why do XeF4 and CF4 have different shapes even though
the central atom is coordinated by four Fluorine atoms in both
cases? One way to answer these questions about molecular
structure is to use a simple approach that builds on the Lewis-
Dot structure approach called the Valence Shell Electron Pair
Repulsion Model, or VSEPR model. The idea behind this approach
is that the structure around a given atom is determined
principally by minimizing electron repulsions. That is, the
bonding and non-bonding electrons around a given atom will be
positioned as far apart as possible. For example, BeCl2 has the
Lewis Structure. There are only two pairs of electrons around
Be. The arrangement that puts the bonding electron pairs as far
apart as possible is a linear ar