Symmetry Flashcards
Symmetry element
Property of an object arsing from its shape
Symmetry operation
Act of applying a symmetry element so the end point s indistinguishable
Principle rotation axis
Highest order, Cn
Horizontal mirror plane
Perpendicular to PRA
Vertical mirror plane
Contains PRA
Identity
E, all molecules possess this
Improper rotation axis
S, rotate and reflect
Inversion centre
I, each point moves through the inversion centre and out the other side
Point group of very high symmetry molecules
Octahedral, Oh or tetrahedral, Td
Point group of molecules with E only
C1
Point group of molecules with E and mirror plane only
Cs
Point group of molecules with E and I only
Ci
How to determine point group
Check if high or low symmetry
Find PRA, C2 perpendicular = D, no C2 perpendicular = C
Has σh = h in subscript
Has σv but no σh, use v in subscript if Cn, d in subscript if Dn
No mirror planes = no letter in subscript
Value f functions the same after applying symmetry operation
+1
Value if functions changes positon but not sign or direction after applying symmetry operation
-1
