CHEM 320 - lecture13 - Simple bonding theory & Symmetry

symmetry elements

geometrical entity such as a line, a plane, or a point, with respect to which one or more symmetry operations can be carried out

symmetry operation

a movement of a body such that the appearance after the operation is indistinguishable from the original appearance

AKA after moving the elements around, the molecule shoudl look the same

E

identity operation

all molecules have it by existing

Cn

rotation by 360/n degrees around a n-fold symmetry axis

Ex: C2 means a rotation axis that you rotate 180 degrees around

σ

reflection operation across a mirror plane

exchange of points through a plane to an opposite and equidistant point

i

inversion of a molecule about a center/point of inversion

each point moves through a common central point to a position opposite and equidistant

Sn

rotation by 360/n degrees followed by reflection perpendicular to rotation axis

n-fold axis of IMPROPER ROTATION

principal axis of rotation

the axis of rotation with the HIGHEST n value (Cn)

trigonal planar

___ molecules often have a C3 principal axis of rotation and additional C2 rotation axes through the outer atoms

linear

__ molecules tend to have a principal rotation axis of infinite order/value C_infinity

σv

mirror plane CONTAINING principal axis of rotation

vertical plane

σd

mirror plane CONTAINING the principal axis of rotation but NOT the outer atom

σh

mirror plane PERPENDICULAR to principal axis of rotation