• Resonance: is used when more than one valid Lewis structure can be written for a molecule (can move a double bond between the same elements)

             ○ Actual electron structure of the molecule is an average of these resonance structures

  • Equal contribution of resonance structures make a molecule nonpolar
  • Bond order:

            ○ Single bond has BO of 1; Double bond has BO of 2 → length of single bond is longer

  • Ex.

            ○ Double bond isn’t either left or right, but rather split between two locations

             ○ The bond order of N is 1.5 (3 bonds are split between 2 locations)

  • Note: questions involving bond length will often involve resonance → have to draw out all resonance structures and use double arrows to indicate that the real molecule is an avg of all three

Formal Charge

Formal charge can be used when there are diff lewis structures that can be drawn for a molecule

  • Best Lewis structure will have a sum of formal charges equal to 0

           ○ On AP exam will usually have 2 already drawn structures and ask which one is more valid

  • Formal Charge = Valence Electrons – (Lone pairs [dots] + Bonded pairs [lines]
  • What if they have the same number of zeroes?

          ○ The “better” structure has the more negative charge on the more electronegative element