2. The symmetry of molecules and solids is a very
powerful tool for developing an understanding of
bonding and physical properties
– Used to predict the nature of molecular orbitals
– Used to predict if electronic and vibration
spectroscopic transitions can be Observed
We will cover the following material:
Identification/classification of symmetry
elements and symmetry operations
Assignment of point groups
Identifying polarity and chirality using point
groups
3. Polar Molecules
A molecule cannot be polar if it has
1. a center of inversion
–any group with i
2. an electric dipole moment
perpendicular to any mirror planes
–any of the groups D and their
derivatives
3. an electric dipole moment
perpendicular to any axis of rotation
–the cubic groups T, O, the
icosahedral I, and
their modifications
4. Chiral Molecules
A molecule is not chiral if
1. it posses an improper rotation
axis Sn
(this includes mirror planes an
inversion
centers)
2. it belongs to the group Dnh or
Dnd
3. it belongs to Td or Oh
