This preview shows page 1. Sign up to view the full content.
Unformatted text preview: -bonding electrons (hence the "EP" part of VSEPR, the "electron pair").
Therefore, instead of looking at single electrons, we deal with each electron pair (cuts our work
in half right off the bat!).
Finally, we notice that, with the correct spin configuration, we can fit two electrons into a
given orbital, but that, because the region of space defined by the orbital is occupied by
negatively charged particles (electrons), that region of space has a negatively charged
characteristic. Sure, the net charge for the electrons is counterbalanced by the positive protons in
the nucleus, but the region of space occupied by the electrons is negative by virtue of the
particles in that space, just as the region of space occupied by the nucleus is positive by the same
Dakota State University Page 103 of 232 Experiment 9: VSEPR General Chemistry I and II Lab Manual Well, seeing that the region of space around the nucleus of the atom occupied by
electrons is negative in charge, we notice that these electron pairs will repel one another (the last
part of VSEPR, "R" is the repulsion of the valence shell electron pairs). Since these electron
pairs repel one another, we arrive at the premise of VSEPR: electron pairs will arrange
themselves in space about an atom such that their total repulsive energy is minimized.
Well, it sounds more difficult than it really is.
Simply speaking, the electron pairs will get as far apart from one another as possible. By
doing so, their repulsive energy is minimized. Suppose you had to take a particularly foul tasting
medicine, and you were told that you would have to take this medicine for at least 30 days. This
is rather open ended, because we never said "at most" how long you should have to take it, so
you have your choice of 30 days to the rest of your days. What would you choose? Assuming
it's not a life-threatening condition, you would choose to minimize the repulsion as much as
possible. Electrons minimize their repulsion by getting as far apart from one another as possible.
VSEPR mechanics I: The Lewis-Dot Structure
We begin by determining the Lewis-Dot structure of the molecule. We cannot proceed
without the Lewis-Dot structure, because it is from the Lewis-Dot structure that we determine
the number of lone pairs of electrons and how the elements are bonded to one another. It is
important to note that although the Lewis-Dot structure does provide us with bonding
information, it does not speak to the true three-dimensional structure of the molecule.
Although there are some molecules restricted to a plane (two-dimensional), typically they are
three dimensional figures, as we would expect. Since we draw Lewis-Dot structures on paper,
we are confined to two dimensions. Therefore, although we gain a wealth of information from
Lewis-Dot structures, actual molecular shape is not one of the pieces of information Lewis-Dot
VSEPR mechanics II: The Central Element
Now, we must define...
View Full Document