(Polar molecules, Non-polar molecules, etc.)
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if when you consider what Atom to make a lone pair you consider the bond angles in reference to the other atoms why don't we take one from the axial plane say from a trigonal bipyramidal because its bond angle is 90 compared to the equitorial plane one of 120?
The equatorial plane bonding electrons will be made into lone pairs first because they only have bond angles to 2 other bonding pairs at 90 degrees in contrast to the axial bonding regions which have bonding angles to 3 other bonding regions at 90 degrees. So, to minimize repulsion, since lone pair-bonding pair repulsion is greater than bonding pair-bonding pair repulsion the lone pairs will first be placed in equatorial positions.
You would also want to take from the equatorial position and not the axial position because a lone pair in the equatorial position results in the molecule having lower energy. Lower energy is what most molecules strive for too.
One lone pair is first placed in one of the three equatorial positions surrounding an atom in a trigonal bipyramidal electron arrangement because the lone pair will cause the least repulsion there. If placed in an axial position, the lone pair will repel the three equatorial atoms strongly, as opposed to the two equatorial atoms it will strongly repel in an equatorial position.
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