Inorganic Quiz 3

Using Symmetry
predict IR
spectra, dipole moments, the orbitals used in bonding,predict optical activity, interpret electronic spectra
Symmetry elements
used to described the symmetry
of a molecule or ion even if no symmetry is present
symmetry operation
The act of conducting the symmetry element
Identity
consists of no change. Every molecule
has this element
rotation axis
which a 360o/n rotation
results in a molecule indistinguishable from the original. This is also
called an n-fold rotational axis and abbreviated Cn. A molecule can have
more than one symmetry axis; the one with the highest n is called the
principal axis, and by convention is assigned the z-axis
Plane of symmetry
is a plane of reflection through which an
identical copy of the original molecule is given. This is also
called a mirror plane and abbreviated ?. A symmetry plane
parallel with the principal axis is dubbed vertical (?v) and one
perpendicular to it horizontal (?h). A third type of symmetry
plane exists: if a vertical symmetry plane additionally bisects
the angle between two 2-fold rotation axes perpendicular to
the principal axis, the plane is dubbed dihedral (?d).
Center of symmetry
or inversion center, abbreviated i. A molecule has
a center of symmetry when, for any atom in the molecule, an identical
atom exists diametrically opposite this center an equal distance from it.
There may or may not be an atom at the center.
Rotation-reflection axis
an axis around which a rotation by 360o/n,
followed by a reflection in a plane perpendicular to it, leaves the
molecule unchanged. Also called an n-fold improper rotation axis, it is
abbreviated Sn, with n necessarily even.
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