How to determine shape

[Ethan_Lee_1E]

How do you know the difference of a whether a molecule will br trigonal planar or pyramidal? Why do molecules with the same amount of atoms involved have different shapes?

[Kelly Puhawan 1H]

You can tell the difference by looking at how many regions of electron density a molecule has! This is especially important when determining whether a molecule is trigonal planar or trigonal pyramidal by counting regions of electron density. A lone pair can also be considered one of these regions just as a normal bond is.