Trigonal Planar ( AX3)
The Trigonal Planar shape is a type of shape which a molecule takes form of when three bonds point to corners of an equilateral triangle. The atoms are in the same plane, and bond angles are 120 degrees. The trigonal planar shape is symmetrical, therefore making it non-polar. Some examples of the trigonal planar shape molecules would include:
Boron Hydride
Carbonate Ion
What contributes to this shape?
The only thing that contributes to this shape are the three bonds which the central atom is attached to. There are no lone pairs of electrons which would repel with the surrounding atoms and provide a different bond angle and shape. Since there are only three bonds attached to it and no lone pairs, the bond angles tend to be 120 degrees due to the inability to bend.
Bent (AX2E)
The Bent shape also known as angular, is a type of shape which a molecule takes form of when there are two bonds attached to the central atom along with 1 lone pair. This bent shape falls under the trigonal planar shape, because if you were to remove one bond off the trigonal planar molecule, it would form a bent shape. The molecule is polar since it is asymmeterical and bond angles are less than 120 degrees. Here are some examples of the bent shape molecule:
Sulfur Dioxide
Ozone
Note: Ozone forms a resonance structure meaning that it can exist in either of the two forms shown above
What contributes to this shape?
The only thing that contributes to this shape are the two bonds which the central atom is attached to and a lone pair. The lone pair of electrons repel with the electrons which are on the surrounding atoms, causing the bonds to slightly bend. This bend provides the bond angle of less than 120 degrees.