1. Delocalized Pi Bonding
Resonance Structures
Delocalized Pi Bonding

2. How can I predict a structure will have delocalized bonding?
The traditional strategy for drawing the Lewis structure doesn’t work (C, N, or O have too many electrons).
When using the longer strategy (see final slide), we find multiple options for forming a double bond with the central atom.

3. How can I predict a structure will have delocalized bonding?
Each of those options represents a resonance structure.
None of the resonance structures are correct.
We can use the resonance structure to predict hybridization, shape, and number of sigma and pi bonds.
Instead, the actual structure is essentially the average of the resonance structures.
The pi bond(s) are shared over multiple bonding locations, resulting in fractional bond orders.

4. Delocalized pi bonding in NO3-

5. Long version of Lewis structures
Count total # of valence electrons (be sure to account for charge).
Draw structure using single bonds only.]
Add lone pairs of electrons to give outer atoms an octet.
Any remaining electrons go on central atom.
Move electron pairs to form double/triple bonds, if necessary.