This is in response to a recent question about bonding within the CH2OO molecule: CH2OO bonding
Scroll to the second article in the Sandia newsleter found here Here is a YouTube interview with the researchers.

Discussion of bonding in SO3.
Which Method of Assigning Bond Orders in Lewis Structures Best Reflects Experimental Data?
An Analysis of the Octet Rule and Formal Charge Systems for Period 2 and 3 Nonmetallic Compounds
The JCE article by Ronald See. Additional supplementary material

Why do two electrons occupy the same orbital? Here is a one page activity that involves some paper folding to show how the magnetic lines of force could overlap so that two electrons can occupy the same orbital. It's an oversimplification, yes, but it gives some justification for electron pairing.

Bonding: Ideal bonds are either "ionic" or "covalent", but there are very few ideal bonds. (Actually only the diatomic, homonuclear molecules have completely covalent bonds.) Instead, "real bonds" have characteristics of the two extremes. This spreadsheet determines the percent ionic character in a bond.
Percent ionic character calculator

GradeCalc is a spreadsheet to use for calculating and curving grades. (Excel) - 06/02/12

Searching the Curriculum Framework (07/09/12)