Lone Pairs on VSEPR Model

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Hannah Pham
Posts: 104
Joined: Fri Aug 09, 2019 12:17 am

Lone Pairs on VSEPR Model

Postby Hannah Pham » Sun Nov 17, 2019 9:58 pm

How do you know if a lone pair lies on the axial or equatorial position?

Daniel Chen 2L
Posts: 101
Joined: Fri Aug 30, 2019 12:15 am

Re: Lone Pairs on VSEPR Model

Postby Daniel Chen 2L » Sun Nov 17, 2019 10:00 pm

Lone pairs are only supposed to be on the equatorial positions because those are the most stable I think.

Helen Struble 2F
Posts: 97
Joined: Sat Aug 24, 2019 12:17 am

Re: Lone Pairs on VSEPR Model

Postby Helen Struble 2F » Sun Nov 17, 2019 10:06 pm

The example we talked about in class was for the "see-saw," or AX4E. This geometry is the same as trigonal bipyramidal except one of the axial atoms is instead a lone pair. Lone pairs have higher repulsion, so the lowest energy structure is one in which the lone pair is in the place of an axial atom, not an equatorial atom. The closer electrons are together, the less stable the structure. So, putting the lone pair in place of an axial atom is more stable because the nearest regions of electron density are 90 degrees away, and there is only two of them. If it was in an equatorial space, the nearest regions of electron density would also be 90 degrees away, except there are three of them. Having two regions at 90 degrees is more stable than having three, so the lone pair occupies an axial space.


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