CH301H - Principles of Chemistry I: Honors
Fall 2011, Unique 51040

Lecture Summary, 1 November 2011

Atomic Orbital Hybridization:s and p orbitals in the valence shell are close enough in energy that they can mix to form a new set of atomic orbitals, called hybrids.  Hybrid orbitals allow atoms to form multiple bonds that are as far apart from each other in space as possible, which allows the molecule to achieve the lowest energy configuration.  When considering the 2s and 2p orbitals, the possible mixing that we achieve depends on how many atoms or lone pairs the central atom is bonded to (i.e. what we called the steric number back when talking about VSEPR).

   SN    AO's           hybrids
   2        s + p           sp, sp
   3        s + 2 p        sp2
   4        s + 3 p        
sp3, sp3, sp3, sp3

To first order these hybrid orbitals all look the same, and differ only how the are arranged around the central atom to maximize the space between them.  The arrangement of hybrid orbitals around the central atom leads to the characteristic molecular geometries that we have already encountered when talking about VSEPR.