Hybridization

by James

Organic chemistry is primarily going to be about moving around electrons. I often say that electrons are to chemistry what currency is to economics. 

In order to understand how electrons move around, we first need to know where they are.

Electrons “live” in 3-dimensional areas of space called “orbitals”. The exact shapes and energies are determined by an equation called the Schroedinger equation, but you can kind of imagine them like seats on an Indian bus.

For the purposes of organic chemistry, we’re only going to care about two types of orbitals. S orbitals and p orbitals.

S orbitals look like spheres.

p orbitals look like dumbbells (There’s an area with zero electron density in the middle. That’s called a “node”).

Every atom has three p orbitals, which are oriented at 90 degrees to each other.

So boron, carbon, nitrogen, oxygen, etc. each have one s and three p orbitals (4 total)

One question: how do we jive this with the 4 identical C-H bonds we see at 109 degrees for methane?

One common approach is called “hybridization” . It’s a bit of a kludge, but it gets us where we need to go.

  • We’re going to take the s orbital and mix it together with a certain number of p orbitals (1, 2, or 3). The total number of orbitals (s + p) will give us the total number of hybrid orbitals.
  • All the hybrid orbitals will be identical, and will orient themselves the maximum distance apart (tetrahedral in the case of CH4).
  • Any p orbitals that aren’t part of the hybrid will be “left over” as unhybridized p orbitals.

Still confused? Think of this analogy.

Imagine that you have one 2 L bottle of Sprite and three 2 L bottles of Pepsi. So 4 bottles total. Imagine we pour all the Sprite and Pepsi out, mix them together, and then re-fill the bottles. We’d now have 4 identical bottles of pop that have 25% Sprite character and 75% Pepsi character. (sp3).

Alternatively we could just mix  two of the Pepsi bottles with the Sprite, which would give us 3 bottles with 33% Sprite character and 66% Pepsi character (sp2), leaving behind one  “unhybridized” Pepsi (p).

Or if we hybridized just one Pepsi, we’d have two bottles with 50% Sprite and 50% Pepi character (sp), and TWO unhybridized Pepsis left over (p).

The table (below) has some examples.

Thanks for reading! James