Which of the following correctly describes the resonance structures of the sulfur dioxide (SO_2) molecule?

• A. SO_2 has three resonance structures, each with a different atom carrying a formal positive charge.
• B. SO_2 has only one stable Lewis structure with two S–O single bonds and no resonance.
• C. SO_2 has resonance structures where the sulfur atom carries a negative formal charge in all forms.
• D. SO_2 has two major resonance structures, each with one S=O double bond and one S–O single bond, with the negative charge delocalized over the oxygen atoms.

Answer: (D)

Verified step by step guidance

1. Recall that resonance structures are different Lewis structures for the same molecule that differ only in the placement of electrons, not the arrangement of atoms.
2. Draw the Lewis structure of SO_2 by counting valence electrons: sulfur has 6 valence electrons, each oxygen has 6, so total valence electrons = 6 + 2*6 = 18 electrons.
3. Construct possible Lewis structures with sulfur in the center bonded to two oxygens, and distribute electrons to satisfy the octet rule as much as possible, considering double bonds and lone pairs.
4. Identify resonance structures by moving the double bond between sulfur and one oxygen to the other oxygen, resulting in two major resonance forms where sulfur has one double bond and one single bond to oxygen.
5. Determine formal charges for each resonance structure to confirm that the negative charge is delocalized over the oxygen atoms, and sulfur typically has a formal charge of zero or positive, consistent with the correct resonance description.