Which of these resonance structures for SO4^2- is least favorable? O=S=O O-S-O What is the bond order for S-O bonds in the correct valence structure above? 1.5
The Correct Answer and Explanation is:
The least favorable resonance structure of the sulfate ion is structure A. This is because structure A has two double bonds and two single bonds, leading to an uneven distribution of charge among the oxygen atoms. The correct resonance structures should distribute the negative charge symmetrically across all four oxygen atoms, making the ion more stable.
For the sulfate ion, resonance occurs when multiple valid Lewis structures can represent the electron distribution. The formal charge calculations reveal that the most favorable structures minimize charge separation while allowing the negative charge to be evenly distributed. Structure A, with two distinct double bonds, causes an uneven charge distribution, making it less favorable.
The bond order for sulfur oxygen bonds in the correct valence structure is 1.5. Bond order is calculated by averaging the bond types across resonance structures. In the case of sulfate, sulfur is surrounded by four oxygen atoms. Instead of having two single bonds and two double bonds in a single static structure, resonance spreads the electron density across all four bonds. This results in partial double bond character in each sulfur oxygen bond. The bond order calculation follows the formula:
Bond Order = Total Bonding Pairs ÷ Total Equivalent Bonds
For sulfate, resonance creates an equal distribution of four bonding pairs over four equivalent sulfur oxygen bonds, yielding a bond order of 1.5. This means each bond is stronger than a single bond but weaker than a pure double bond. The correct valence structure ensures charge delocalization, enhancing the stability of the sulfate ion. This delocalization explains why sulfate exhibits uniform bond lengths for all sulfur oxygen bonds rather than distinct single and double bonds.
