- Principles of Chemistry I: Honors
Fall 2015, Unique 49310
Lecture Summary, 20 October 2015
Molecules: We are now going to use our atomic
orbitals to form molecular orbitals, which will provide the
mechanism of keeping stable electron density between two nuclei,
which will in turn lower the potential energy of the system and
form a molecular bond. The technique that we are going to
use to do this is called "linear combination of atomic orbitals to
molecular orbitals," LCAO-MO. Our coordinate system will be
defined with the internuclear axis lying along the z-axis.
From that simple definition, we spent a lot of time drawing
the structure of s and p orbitals of same and opposite phase and
figuring out what the resulting structure would look like.
These are also drawn in your book, and you should spend some
time getting comfortable with these images.
We also reviewed the naming convention for these orbitals. For each orbital, we need to ask 3 questions about the orbitals shape and phase:
1) Does the MO have cylindrical symmetry around the internuclear (z) axis?
2) Is the MO symmetric with respect to inversion?
yes: g (for "gerade" (even))
no: u (for "ungerade" (uneven))
3) Is there a nodal plane perpendicular to the internuclear (z) axis in the center of the molecule?