Point group

atomic spectra

1. SYMMETRY ELEMENTS,OPERATION AND POINT GROUP SUBMITTED TO: Dr. (Mrs.) Beena Bhatia SUBMITTED BY: Vishal Kumar Jangid M.Sc Final (Physics)-2017

2. Symmetry operation :  is an action that leaves an object looking the same after it has been carried out. Symmetry Elements : Each symmetry operation has a corresponding symmetry elements which is the axis, plane line or point with respect to which the symmetry operation is carried out. Symmetry operation and elements

3. Table of Elements and Operations Element Operation Symbol Identity Identity E Symmetry plane Reflection in the plane σ Inversion center Inversion of a point x,y,z to -x,-y,-z i Proper axis Rotation by (360/n) o C n Improper axis 1. Rotation by (360/n) o 2. Reflection in plane perpendicular torotation axis S n

4. Simplest symmetry operation. All molecules have this element. If the molecule does have no other elements, it is  asymmetric.  It does nothing to the molecules . CHFClBr identity

5. If we rotate the molecule about a particular axis , then there exist a indistinguishable form. n= (360 )/ (angle with which molecule rotate) Proper axes of rotation ( C n )

6. A point at the center of the molecule . ( x,y,z ) to (-x,-y,-z).  Inversion, Center of Inversion ( i )

7. Molecules contain mirror planes . σ h (horizontal):  plane perpendicular to principal axis σ d (dihedral),  σ v (vertical):  plane linear with principal axis σ d :  σ   parallel to C n  and bisecting two C 2 ' axes σ v : Vertical, parallel to principal axis Planes and Reflection ( σ )

8. This is a compound operation combining a rotation ( C n ) with a reflection through a plane perpendicular to the C n  axis  σ h .( C n  followed by  σ h ) σC n = S n Rotation-reflection, Improper axis ( Sn )

9. It is only possible for certain combinations of symmetry elements to be present in a molecule  . we may group together molecules that possess the same symmetry elements and classify molecules according to their symmetry . These groups of symmetry elements are called  point groups   Point grou p

10. linear low symmetry? No C n  axis? Yes- Principal axis C 3  passing through B. nC 2  axes? Yes 3C 2  axes σ h ? Yes  D 3h BF 3

11. THANK YOU