Difference in models

[ConnorRazmaDis2I]

What causes a molecule to either form into a Trigonal planar, Trigonal pyramid, or a T-shape?

[Kyleigh Follis 2H]

A molecule will be trigonal planar if it has 3 pairs of bonding electrons around the central atom. It will be trigonal pyramid if it has 3 bonding pairs of electrons and 1 lone pair of electrons around the central atom. It will be T-shape if it has 3 bonding pairs of electrons and 2 lone pairs of electrons around the central atom.

[Brian Cook]

Building on what Kyleigh has said, pay attention to the VSEPR formula which is based on the central atom, number of atoms sharing bonds, and number of lone pairs on central atom. Structures with the same formula will take on the same shape, so once you solve for one, you can assume that following structures with that formula will also take in that shape. Hope this helps :)