Why are lone pairs in the trigonal bipyramidal electron domain geometry placed in the equatorial positions?

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I need help understanding the following statement in my book (regarding trigonal bipyramidal geometry):

Placing a lone pair in an axial position would put it at 90 degree to three other electron domains. Placing it in an equatorial put is at 90 degree to only two other domains, thus minimizing the number of strong repulsive interactions

What does it mean by "90 degree" to two/three "domains"?

Postby miznaakbar » Sun Nov 19, 2017 10:10 pm

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.