trigonal planar
generic formula: AX3
example: borane BH3
If there are no lone pairs then the molecular geometry matches the electronic and is trigonal planar. The base bond angle is 120° and there is no reason to tweak the bond to another value.
POLARITY: NON-POLAR - As long as all three positions are the same, then the molecule cannot be polar due to perfect symmetry.
bent or angular
generic formula: AX2E
example: ozone O3
If there is one lone pair on this electronic geometry, the molecular geometry is now bent or angular. The base angle is 120° while the tweaked angle will now be slightly less (118°) due to the extra repulsion from the lone pair.
POLARITY: POLAR - The lone pair electrons throw off the perfectly cancelling symmetry of the three trigonal planar regions thus making the molecule polar.