2.2.14
HL
ONLY
Formal Charge
Selecting the preferred Lewis structure.
Calculation Formula
FC = (Valence e⁻) − (Non-bonding e⁻) − ½(Bonding e⁻)
Selection Rules
- The preferred structure has formal charges closest to 0.
- If charges exist, negative FC should be on the most electronegative atom.
Worked Example: OCN⁻
Consider two possible structures for the Cyanate ion:
Structure A (Preferred)
[:O=C=N:]⁻
FC: O=−1, C=0, N=0
Negative charge on electronegative O
Structure B (Less Preferred)
[:O≡C−N:]⁻
FC: O=0, C=0, N=−1
Negative charge on less electronegative N