Steric Number - Steric Number in VSEPR

Steric Number in VSEPR

Calculating the steric number of a molecule's central atom is a vital step in predicting its geometry by VSEPR theory. On the molecule SF₄, for example, the central sulfur atom has four ligands about it, calculated by considering sulfur's coordination number. In addition to the four ligands, sulfur also has one remaining lone pair (expanded octet does not apply in this compound). Thus, the steric number is 5. The central atom's steric number together with the number of lone pairs allows one to predict the geometry of that central atom, using the table of molecular geometries for the VSEPR theory.