Week 2: February 12 – 14 th
Resonance and Electron Pushing
What is it?
Resonance is a theory proposed by Linus Pauling to accurately depict molecules that
could not be drawn with a single Lewis structure. For example, consider the following
acetate ion (chemical formula C H 2 3: 2-
Which one is correct? Chemical testing shows these bonds are shorter than single bonds
but long than double bonds; also, both oxygens have a slight negative charge. So, how
does one know which oxygen be drawn with negative charge and which should have the
lone pair? The answer, of course, lies in resonance structures.
Resonance structures are a combination of different Lewis Structures that contribute to
make a real hybrid molecule. In other words, two or more ‘fake’ Lewis Structures
combine to make the ‘real’ picture. Don’t be fooled by the method of drawing resonance
structures and multiple different figures: resonance structures DO NOT actually exist!
My chemistry teacher in high school described resonance as such: You want to show
someone a unicorn. But you can’t find a unicorn. So instead you show them a horse and a
rhinoceros and tell them a unicorn is a mixture of both. Other people like the 2 colors of
paint mixing to make a new color metaphor; I’m personally fond of the unicorn.
How to draw Resonance Structures
The following list of rules describes a good checklist you can go through for each
resonance structure to make sure it is correct. With practice these rules will become
1. Connectivity of the atoms does not change. Resonance is the sharing of electrons in π
orbitals (double bonds) and p orbitals (lone pairs). Never break sigma (single) bonds!
2. All contributing structures have the same number of valence electrons.
3. Obey the rules of covalent bonding. No Texas Carbons! Priority Rules