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lone pairs in trigonal bipyramidal shape

Posted: Mon Nov 13, 2017 4:29 pm
by Lindsay H 2B
Why is it that when there are five regions of e- density but 2 of them are lone pairs on the central atom (such as ICl3 in ex 4.9a) both lone pairs are in the equatorial positions rather than the axial positions? I thought that the point was to keep lone pairs as far apart as possible, and if 2 lone pairs took the 2 axial positions, they would be farther away from each other than in 2 of the equatorial positions.

Re: lone pairs in trigonal bipyramidal shape

Posted: Mon Nov 13, 2017 4:45 pm
by Cooper1C
See figure 4.5 in the textbook (page 115): "If the lone pairs had taken the axial positions, they would have been at 90 degree angles from the equatorial positions, resulting in greater repulsion."

Re: lone pairs in trigonal bipyramidal shape

Posted: Mon Nov 13, 2017 7:09 pm
by Elizabeth Ignacio 1C
If the lone pair is axial, it interacts with three atoms instead of the (only) two atoms it would interact with as an equatorial. As an equatorial lone pair, it would just interact with the axial atoms. The molecule prefers this because it takes less energy.