[Dolphinsiu]

Actually I only would like you to check whether my answer is right or not in the following questions:

Determine the point group of the following compounds:

PF5: D3h
Staggered form of ethane: D3v
[Co(en)3]3+: D3
NH3: C3v
1,3,5,7-tetrafluorocyclooctatetraene: C2

[Alpha-Omega]

In order to verify these you will have to perform the symmetry operations and determine which group each molecule belongs to. 

That is why I directed you to the interactive symmetry sites where you can make those determinations interactively.

Your other option is to build the models with a molecular model kit and perform the indicated operations for the point groups and validate the group to which each of your species belongs.

You have to classify these molecules to their respective point groups by performing the symmetry opearations.


"PF₅: D_3h"

The PF₅ molecule structure belongs to the D_3h  symmetry point group. Its major axis is C₃, which gives you the number 3 for the point group. It has a C₂ axis perpendicular to the major C₃, so it is D group. It has σ_h plane symmetry, so it is D_3h.


“Staggered form of ethane: D_3v”

For the staggered form of ethane I think you mean D_3d (I think that D_3v is a typo?).

The staggered C₂H₆ molecule structure belongs to the D_3d point group. Its major axis is C₃, which give us the number 3 for the point group. It has a C₂ axis perpendicular to the major C₃, so it is D group.  It has no σ_h plane, but it does have σ plane symmetry, so it is D_3d.

You can also verify that here (just perform the symmetry operations to verify the point group D_3d 

http://www.phys.ncl.ac.uk/staff/njpg/symmetry/Molecules_l3d.html


"[Co(en)₃]₃⁺: D₃"

In order to validate that this molecule belongs to the D₃ point group you will have to validate the following:

1. Linear, low symmetry or high symmetry? No
2. C_n axis? Yes- Principal axis C₃
3. nC₂ axes perpendicular to C₂? Yes
4. σ_h? No
5. σ_d? No

D₃ applies for "[Co(en)₃]₃⁺


“NH₃: C_3v”

The Point Group C_nv:

In general, molecules in the point group C_nv all have a principal axis of rotation, C_n, but unlike the D_n, D_nh, and D_nd groups, do not have nC₂ axes at right angles to it. Many common molecules belong to this point group, including H₂O, NH₃.

You can check the NH₃ here (just run thru the operations to verify the C_3V point group): 

http://www.phys.ncl.ac.uk/staff/njpg/symmetry/Molecules_l3d.html

"1,3,5,7-tetrafluorocyclooctatetraene: C₂"

In order to validate that this molecule belongs to the C₂ point group you must show the following:

Molecule possesses one axis of symmetry only (C₂) plus it possesses no other elements except C₂.

[Dolphinsiu]

Thanks a lot, Alpha-Omega!

[Alpha-Omega]

NP