CHEM320-lecture14-Symmetry & Point groups

point group

set of symmetry elements/operations

molecules with the same set of symmetry elements belong to the same point group

role is to classify infinite number of molecules into relatively common “families”

point groups with mirror planes

Cnh, Cnv, Dnh, Dnd

point groups with no mirror planes

Cn, Dn

point groups of low symmetry

C1, Cs, Ci

point groups of high symetry

Cinfinity,v

Dinfinity,h

Td

Oh

Ih

D classification

nC2 axes perpendicular to the Cn principal axis of rotation

n-fold principal rotation axis PLUS n 2-fold rotation axes perpendicular to it

C classification

indicates only 1 rotational axis