Question

Question #06590

Answer 1

The only possible molecular shape for a nonpolar AY₃ is trigonal planar. Trigonal pyramidal and T-shaped molecules are impossible.

There are four possible electron geometries for an AY₃ molecule.

They could be AY₃, AY₃E, AY₃E₂, or AY₃E₃.

AY₃

An AY₃ molecule is trigonal planar.

The A-Y bond dipoles will all cancel, so the molecule will be nonpolar.

AY₃E
An AY₃E molecule is trigonal pyramidal.

The A-Y bond dipoles all have a component pointing in the same direction, and there is nothing to counteract the dipole from the lone pair.

An AY₃E molecule is polar.

AY₃E₂

An AY₃E₂ molecule is T-shaped.

The polar A-Y bond dipoles cancel each other, but it is unlikely that the equatorial A-Y bond will cancel the effect of the lone pairs.

An AY₃E₂ molecule is polar.

AY₃E₃

An AY₃E₃ molecule is T-shaped.

The polar A-Y bond dipoles cancel, and two of the equatorial lone pairs cancel, but it is unlikely that the equatorial A-Y bond will cancel the effect of the equatorial lone pair.

An AY₃E₃ molecule is polar.

So, the three possible molecular shapes are trigonal planar, trigonal pyramidal, and T-shaped, but only the trigonal planar shape is nonpolar.