Point Groups ppt pdf.pdf

Easy and imp

1. POINT GROUPS
By,
Dr. PrajaktaS. More
Smt. CHM College, Ulhasnagar

2. Sr.
No.
Point
group
Characteristic Symmetry
elements
Example
1.C
2v C
2, 2σv and E H
2O
2.C
3v C
3, 3σ
vand E NH
3
3.C
2h C
2, σ
h, i and E trans-dichloro
ethylene
4.D
3h C
3, 3C
2, 3σv, σh, S3and EBCl
3
5.C
∞v C
∞, ∞σ
v and E HCl
6.D
∞h C
∞, ∞C
2, ∞σ
v, σ
hand EH
2
Point groups: It is a collection of all symmetry elements that can be
carried out on a molecule belonging to that group.

4. CnvPoint group: Cn, nσv, E
C2vpointgroup:ItiscollectionofC2,2σvandE
symmetryoperations.e.g.Watermolecule.

6. C3v point group: It is collection of C3, 3σVand E symmetry
operations. e.g. Ammonia molecule

8. Cnhpoint group: Cn, σh, i, E
C2hpoint group:It is collection of C2, σh, i and E
symmetry operations. e.g. Trans dichloroethylene

10. Dnhpoint group: Cn, nC2, nσv, σh, E
D3hpoint group:It is collection of C3, 3C2, 3σv, S3, σh
and E symmetry operation. e.g. BCl3molecule.
Three vertical plane of
symmetry 3σv
One horizontal plane of symmetry σh
C3axis perpendicular to
three C2axes

11. Point groups of linear molecules:
C∞vpoint group:
It contains C∞, ∞σv and E
symmetry operation.
e.g. Hetero nuclear
diatomic molecule like
HCl
D∞hpoint group:
It contains C∞, ∞C2, ∞σv,
σh, i and E symmetry
operations.
e.g. Homonuclear
diatomic molecule like H2

12. Additional points

13. Classificationofpointgroups:
Elements Pointgroup Example
C type point group
Cn Cn H2O2
Cn+ nσv Cnv H2O,NH3
Cn+ σh Cnh Trans dichloro
ethylene
D type pointgroup (possess Cnperpendicular to C2 axis)
Cn+ nC2 Dn [Cu(en)2]
+2
Cn+ nC2+ nσV+
σh
Dnh BCl3
Cn+ nC2 + σd Dnd Allene
Higher symmetry point groups
Tetrahedral Td CH4, CCl4
Octahedral Oh SF6

14. Orderof
group
Point
group
Characteristic Symmetry
elements/ operations
Example
4 C
2v C
2, 2σv and E H
2O
6 C
3v 2C
3, 3σ
vand E NH
3
4 C
2h C
2, σ
h, i and E trans-dichloro
ethylene
12 D
3h 2C
3, 3C
2, 3σv, σh, 2S3and EBCl
3
∞
C
∞v C
∞, ∞σ
v and E HCl
∞
D
∞h C
∞, ∞C
2, ∞σ
v, σ
hand E H
2
Order of group: The total number of symmetry elements present in the
group is called order of group and it is denoted by h.

15. Ammonia (as well as BCl
3) has only one C
3axis, then how 2C
3, if order of
group is to be calculated?
Ans: Yes ammonia has only one C
3axis. However, one C
3axis can produce
three C
3operations namely
•120º rotation i.e. C
3
1
•240º rotation i.e. C
3
2
•360º rotation i.e. C
3
3
( it is identity E )
Out of these three, 120º rotation and 240º rotation represents 2C
3and
360ºrotation represents E