Question 4.12: Calculating Formal Charges Calculate the formal charge on ea......
Calculating Formal Charges
Calculate the formal charge on each atom in the following electron-dot structure for SO_2:
\underset{..}{\overset{..}{:O \ \ }} – \overset{..}{S}=\underset{..}{\overset{..}{O}}STRATEGY
Find the number of valence electrons on each atom (its periodic group number). Then subtract half the number of the atom’s bonding electrons and all of its nonbonding electrons.
For sulfur: Isolated sulfur valence electrons 6
Bound sulfur bonding electrons 6
Bound sulfur nonbonding electrons 2
Formal charge = 6 – \frac{1}{2} (6) – 2 = +1
For singly bonded oxygen: Isolated oxygen valence electrons 6
Bound oxygen bonding electrons 2
Bound oxygen nonbonding electrons 6
Formal charge = 6 – \frac{1}{2} (2) – 6 = -1
For doubly bonded oxygen: Isolated oxygen valence electrons 6
Bound oxygen bonding electrons 4
Bound oxygen nonbonding electrons 4
Formal charge = 6 – \frac{1}{2} (4) – 4 = 0
The sulfur atom of SO_2 has a formal charge of +1, and the singly bonded oxygen atom has a formal charge of -1. We might therefore write the structure for SO_2 as
\underset{..}{\overset{..}{\overset{-}{:}O \ \ }} – \overset{\overset{+}{..}}{S}=\underset{..}{\overset{..}{O}}