Valence Bond Theory and Hybridization

Red = High Density

Valence bond theory

So, what is valence bond theory?  It's when bonds formed by sharing electrons form overlapping atomic orbitals.  As you bring bonded atoms closer and closer together you build up greater electron densities.

Hybridization - mixing of two or more atomic orbitals to form a new set of hybrid orbitals.  This is the bed-time level version, my professor says.  How does this work?

1.) Mix at least 2 nonequivalent atomic orbitals (e.g. s and p).  Hybrid orbitals have very different shape from original atomic orbitals.
2.) Number of hybrid orbitals is equal to number of pure atomic orbitals used in the hybridization process.
3.) Covalent bonds are formed by:
      a. Overlap of hybrid orbitals with other atomic orbitals
      b. Overlap of hybrid orbitals with other hybrid orbitals

Some of these bonds look different.  What are they each called?  A Sigma bond occurs between the two atoms.  A Pi bond appears above and below the plane of nuclei of the bonding atoms.  Single, double, and triple bonds have varying amounts of sigma and pi bonds:

- A single bond has 1 sigma bond.
- A double bond has 1 sigma bond and 1 pi bond.
- A triple bond has 1 sigma bond and 2 pi bonds.

As you can tell, each bond has 1 sigma bond and the pi bond is equal to the type of bond minus 1.  Ergo a triple bond (3 - 1) has 2 pi bonds.

So, how do I predict the hybridization of the central atom?

1.) Draw the Lewis structure of the molecule.
2.) Count the number of lone pairs AND the number of atoms bonded to the central atom.