Location of Lone Pairs

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

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Jonas Talandis
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Joined: Fri Sep 28, 2018 12:16 am

Location of Lone Pairs

Postby Jonas Talandis » Mon Nov 26, 2018 5:12 pm

In lecture, while referencing a molecule with 5 regions of electron density in a trigonal bipyramidal electron region orientation, Dr. Lavelle said that a Lone Pair on the central atom would go in the trigonal plane of the orientation rather than the top or bottom "peaks" of the pyramids because it is more stable to repel the two other atoms in the trigonal plane than to repel all three atoms in the trigonal plane from one of the peaks. Why then, in an octahedral orientation, do the lone pair(s) go on the top or bottom, resulting in a square plane with 2 LPs, if this would repel 4 atoms rather than 3 if the LP were to go in the square plane?

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Re: Location of Lone Pairs

Postby juliasloan_4g » Mon Nov 26, 2018 7:11 pm

Someone asked this question in my lecture, and Dr. Lavelle showed that because octahedral is completely symmetrical no matter where you put a lone pair is is exactly the same. There is no "top" or "bottom." It was easier to visualize when he showed us with his 3D props, but octahedral is the same no matter where the lone pair is put

Jonathan Pai 2I
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Joined: Fri Sep 28, 2018 12:27 am

Re: Location of Lone Pairs

Postby Jonathan Pai 2I » Mon Nov 26, 2018 7:40 pm

Octahedral is 90* between any atom, that's why it doesn't matter. But Trig Bipyr has angles of 90*(axial to equatorials) and 120*(trig planar atoms), that's why LP placement matters in Trig Bipyr.

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