Frost Diagrams
Frost Diagrams are used to help draw the Molecular Orbitals for Valence Bond Structures.
For example, say I have Benzene, and I want to know how many bonding electrons vs. non-bonding electrons it has. Our Valence Bond Structure looks like this:
The first thing we do is draw the shape, with the point (any point) facing down. Then, we draw a circle around it, so that the tips of the shape are touching the edge of the circle.
At every point where the two touch, draw a vertical line.
Now, split the circle in half, horizontally
At this point, we no longer need the original shape, so I'm going to remove it.
What we have here is the skeleton structure for finding the Molecular Orbitals of the structure. Now, we know that Benzene has 6 valence electrons. Let's start assigning them, 2 per line, starting at the bottom.
We draw arrows with single fishhooks on the end to indicate electrons. This is the first level done. Now we split the electrons evenly between the lines on the next level - in this case, 2 each:
Now that we've assigned all of the valence electrons, let's label the lines. Below the line - pi bonds. Above the line - pi anti-bonds. Like so:
And voila! There is your Frost Diagram for Benzene.
I'll put up Frost Diagrams for some other cyclo-molecules later today.