What is the difference between a tetrahedral and trigonal planar molecular geometry?

The main difference between tetrahedral and trigonal planar molecular geometries is the number of atoms bonded to the central atom. In a tetrahedral geometry, there are four atoms bonded to the central atom, arranged in a three-dimensional shape resembling a pyramid with a triangular base. In a trigonal planar geometry, there are three atoms bonded to the central atom, arranged in a flat, triangular shape.