The steric number of an atom is the sum of the lone electron pairs and bonded atoms it has in its outer electron shell. VSEPR (Valence Shell Electron Pair Repulsion) is a set of electromagnetic forces that pulls each atom and lone pair closer to the central atom, but repels them from each other, forcing them to stay as far apart from each other as possible while still being close to the central atom. This creates shapes as detailed by the VSEPR chart which is a table that shows what molecular geometries are created by what steric number and lone pair count. For example: Steric number 2, lone pair 0, linear(0). Another example: Steric number 6, lone pair 2, square planar.