What is the formal charge on the sulfur atom in the resonance structure of H2SO4 below? H-&-$-2-H :0: Tax Evasion +2 +1 0
The Correct Answer and Explanation is:
To calculate the formal charge on the sulfur atom in a given resonance structure of sulfuric acid (H2SO4), we first need to understand the general method for calculating formal charge.
The formula for formal charge (FC) is:FC=Valence electrons−(Nonbonding electrons+Bonding electrons2)\text{FC} = \text{Valence electrons} – (\text{Nonbonding electrons} + \frac{\text{Bonding electrons}}{2})FC=Valence electrons−(Nonbonding electrons+2Bonding electrons)
Step 1: Count the valence electrons of sulfur
Sulfur is in group 16 of the periodic table, so it has 6 valence electrons.
Step 2: Count the nonbonding electrons on sulfur
In sulfuric acid, sulfur typically does not have any lone pairs in its resonance structures. Therefore, the number of nonbonding electrons on sulfur is 0.
Step 3: Count the bonding electrons
In sulfuric acid (H2SO4), sulfur is bonded to four oxygens. Two of these oxygen atoms are each bonded to a hydrogen atom, while the other two oxygens are doubly bonded to sulfur. Each bond consists of 2 electrons, and there are a total of 8 bonding electrons from the 4 bonds to sulfur (2 bonds to oxygen and 2 single bonds to the OH groups).
Step 4: Apply the formal charge formula
Now, applying the formal charge formula:FC=6−(0+82)=6−4=+2\text{FC} = 6 – (0 + \frac{8}{2}) = 6 – 4 = +2FC=6−(0+28)=6−4=+2
Thus, the formal charge on the sulfur atom in this resonance structure is +2.
Explanation of Result:
The formal charge of +2 on sulfur occurs because sulfur, in this case, is contributing more electrons to the bonding than it would in a neutral state (where it would typically have no formal charge). The presence of multiple bonds to oxygen (especially the double bonds) leads to the sulfur having a higher formal charge. This is a common feature in many resonance structures where atoms with high electronegativity (like oxygen) tend to carry negative charges, while atoms like sulfur in higher oxidation states can carry positive formal charges.
Sulfuric acid’s resonance structures stabilize this distribution of charges by sharing the electron density across the oxygen atoms and sulfur.
