seesaw shape

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

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Ruohan Sun 3I
Posts: 19
Joined: Fri Sep 29, 2017 7:07 am

seesaw shape

Postby Ruohan Sun 3I » Sun Nov 19, 2017 11:27 pm

shouldn't the two bonds on the axis be bent because of the repulsion of the lone pair?

Julian Krzysiak 2K
Posts: 49
Joined: Fri Sep 29, 2017 7:07 am

Re: seesaw shape

Postby Julian Krzysiak 2K » Sun Nov 19, 2017 11:58 pm

The see-saw shape is based off of the trigonal bipyramidal, as the molecule in question has 5 areas of electron density. But then you would just need to replace one of the bonds with a lone pair, and in this case it would be the equatorial bond, as you would only be strongly repelling against 2 axial bonds (instead of 3 with the other configuration). I would assume that the atoms on the axis wouldn't be bent because overall, this would preserve energy the best by creating smaller angles. If all 4 atoms were to be pushed downwards, as in a trigonal pyramidal, I think this arrangement would have larger angles throughout, and so wouldn't be as efficient. The see-saw shapes is picked because this way, the atoms are in the best configuration; the angles are at their optimum, of 2 90 degree angles and 120 degree angle, as opposed to the other configuration.

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