General question on Molecular Shape

(Polar molecules, Non-polar molecules, etc.)

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Ashley Odibo Dis3E
Posts: 31
Joined: Wed Nov 15, 2017 3:03 am

General question on Molecular Shape

Postby Ashley Odibo Dis3E » Tue Nov 27, 2018 8:52 am

Generally speaking, when determining the shape of a molecule how can you tell which atoms are going to fall in the same plane?

Fanny Lee 2K
Posts: 73
Joined: Fri Sep 28, 2018 12:29 am

Re: General question on Molecular Shape

Postby Fanny Lee 2K » Tue Nov 27, 2018 9:38 am

I would first draw out the lewis dot structure and use the steric numbers to determine the VSEPR shape of the molecule. If it is linear, trigonal planar, square planar, T shaped, and bent, then it is on the same plane. If the VSEPR shape is drawn using wedges, then it does not lie on the same plane.

Matthew Mar 1J
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Joined: Fri Sep 28, 2018 12:15 am
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Re: General question on Molecular Shape

Postby Matthew Mar 1J » Tue Nov 27, 2018 11:14 am

I think another way to think of it is to count the regions of electron density there are around the central atom and see which regions correspond to atoms that are bonded to the center and which regions are lone pairs.
If you use the notation professor Lavelle used in class (AXE, A=central atom, X=bonded atoms, E=lone pairs), then generally any molecule with X=3 or less will be planar (AX2=linear, AXE3=linear, AX3=trigonal planar, AX2E=bent, AX2E2=bent, AX3E2=T-shape). So molecules with 3 or less regions of electron density from bonded atoms will be planar. The only exceptions are AX3E which is trigonal pyramidal (i.e. not planar), and AX4E2 which is square planar (X>3, but still planar).

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