## Why lone pairs occupy equatorial plane

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

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Joined: Fri Sep 29, 2017 7:07 am

### Why lone pairs occupy equatorial plane

Can someone explain why lone pairs occupy the equatorial plane as opposed to the axial plane? I read the section in the textbook about it, it was talking about achieving lowest energy and the experimental lengths of the bonds in the axial and equatorial plane in a PCL5 molecule, but I just don't conceptually understand this. If someone could put it into simpler terms that'd be awesome, thanks1

Melissa Per 2J
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Joined: Fri Sep 29, 2017 7:04 am

### Re: Why lone pairs occupy equatorial plane

If we look at the bond angles of a trigonal bipyramidal structure, the atoms in the axial plane have a 90 degree bond angle with the three atoms in the equatorial plane. And these atoms in the equatorial plane have a 120 degree bond angle with each other. It is better for the lone pair to be in the equatorial plane because it will have only two 90 degree repulsions from the atoms in the axial plane. Whereas if the lone pair were in the axial plane, it would have three 90 degree repulsions with the atoms in the equatorial plane. I know the angles are going to be a little different because lone pairs have a stronger repulsion... This is how it was explained to me.

miznaakbar
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### Re: Why lone pairs occupy equatorial plane

From what I understand, the explanation above is correct because, in simpler terms, the lone pairs want to be as far away from other regions of electron density as possible since it is more energetically favorable. If the lone pair is on the axial plane, it will be 90 degrees away from 3 regions of electron density; if it is on the equatorial plane, it will be 90 degrees away from just 2 regions of electron density.