Illustrated Glossary of Organic Chemistry

Steric number: The number of atoms, groups, or lone pairs (i.e., electron clouds) around a central atom. The steric number determines molecular geometry.












Carbon dioxide
Steric number = 2
Geometry = linear		   
Boron trifluoride
Steric number = 3
Geometry = trigonal planar		   
Methane
Steric number = 4
Geometry = tetrahedral		   
Phosphorus pentachloride
Steric number = 5
Geometry = trigonal bipyramid		   
Sulfur hexafluoride
Steric number = 6
Geometry = octahedral