SbF5 forms a trigonal bipyramidal shape. There are polar bonds present and I assumed that it is non polar because of it's molecular geometry. However, The molecule itself is not entirely symmetrical (unless I'm thinking of symmetry incorrectly). If I'm not incorrect, can an asymmetrical molecule be non polar?

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    $\begingroup$ A molecule with two non-coincident axes of rotation cannot be polar. $\endgroup$ – Zhe Jan 12 '18 at 16:51
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    $\begingroup$ Why isn't it symmetrical? There are three the equatorial bonds and angle between them is 120° and the axial bonds are there. You have yourself mentioned that it has trigonal bipyramidal shape. Then where is your problem? If you think it is non symmetrical say why. And upload aan image for the same. $\endgroup$ – DJ Koustav Jan 12 '18 at 17:15
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    $\begingroup$ @DJKoustav I think OP is confused about level of symmetry. For example, cube versus sphere. But I think the point they are missing is that a molecule does not need very high symmetry to be non-polar. Just enough. $\endgroup$ – Zhe Jan 12 '18 at 17:47
  • $\begingroup$ @Zhe exactly.....We just need to vectorially add the dipole moments for each bond to get the net dipole moment. And so a symmetry that yields a net dipole of zero is sufficient enough for a molecule to be considered as symmetrical. $\endgroup$ – DJ Koustav Jan 12 '18 at 17:51
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    $\begingroup$ I think I was struggling with picturing it in 3D. When I looked up the shape itself, it just didn't seem entirely symmetrical, but your comments have put it in a different perspective and it clicked. Thanks! $\endgroup$ – Sarah Jan 12 '18 at 20:03

As mentioned in the comments, $\ce{SbF5}$ in the gas phase has a rather high symmetry, the point group looks like $D_\mathrm{3h}$ to me, containing a principal three-fold rotational symmetry axis (along the axial bonds) and three two-fold axis (along each of the equatorial bonds), among other operations. As mentioned in this text, a dipole moment can only coincide with a rotational axis. Since there are four such axis in the molecule, it cannot have a dipole moment.

Note however, that each of the bonds is certainly polar. They just cancel out, as could be proven by vectorial addition of the bond dipole moment.

  • $\begingroup$ Also, pentafluoroantimonate $\ce{SbF5^2-}$ would also have another geometry (distorted square pyramid) and quite a significant dipole moment. $\endgroup$ – andselisk Jan 13 '18 at 4:19

As mentioned in Inorganic Chemistry: Principles of Structure and Reactivity By James E. Huheey, Ellen A. Keiter, Richard L. Keiter, Okhil K. Medhi

enter image description here

The 3D image of SbF5 is as follows: a side view side view

a top view top view The bond dipole moments in vertical axis cancel out .Similarly the three Sb-F bonds positioned at 120 degrees to each other (top view image ) cancel out each other. Therefore SbF5 in non polar molecule.

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    $\begingroup$ Where the atomic coordinates were taken from? $\endgroup$ – andselisk Jan 13 '18 at 4:16

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