Chemical Bonding: Resonance Structures

Chemical Bonding: Valence Electrons

Lewis structures have a major flaw. For many structures (O₃, NO₃^-, etc) drawing a single structure won't show the actual distribution of electrons between atoms. For these structures experimental data tells us a single Lewis structure isn't an accurate picture of the molecule as found in the real world.

To get around this we draw resonance structures. For example, for O₃ we draw:

The actual structure is an average of the two structures. Experimental data tells us that the bonds between the Oxygen atom are actually one and a half (1 ^1/2) and not double bonds.

What you need to know:

• Resonance structures are necessary to show how electrons are distributed in chemical bonds in a molecule.
• Remember, the molecule isn’t flipping back and forth between structures! It's an average of the resonance structures.
• The <---> symbol drawn between resonance structures does not mean equilibrium or any sort of change. It only shows that there is more than one way to draw the structure. It's not a very good choice of symbols, really.