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.