Which of the following Lewis dot structures provides a reasonable representation of SO_2?

• A. O≡S–O with three lone pairs on each oxygen and no lone pairs on sulfur
• B. O–S=O with two lone pairs on each oxygen and one lone pair on sulfur
• C. O–S–O with three lone pairs on each oxygen and two lone pairs on sulfur
• D. O=S=O with one lone pair on each oxygen and one lone pair on sulfur

Answer: (B)

Verified step by step guidance

1. Step 1: Determine the total number of valence electrons available for SO_2. Sulfur (S) has 6 valence electrons, and each oxygen (O) has 6 valence electrons, so total valence electrons = 6 (S) + 2 × 6 (O) = 18 electrons.
2. Step 2: Draw a skeletal structure connecting sulfur to the two oxygen atoms. Typically, sulfur is the central atom because it is less electronegative than oxygen.
3. Step 3: Distribute the valence electrons to satisfy the octet rule for each atom, starting by placing lone pairs on the outer atoms (oxygen) and then on sulfur. Remember that each bond (single, double, or triple) counts as 2 electrons shared between atoms.
4. Step 4: Consider resonance structures and formal charges to find the most stable Lewis structure. Calculate formal charges using the formula: \(\text{Formal charge} = \text{Valence electrons} - (\text{Nonbonding electrons} + \frac{1}{2} \times \text{Bonding electrons})\) for each atom.
5. Step 5: Identify the structure with the lowest formal charges and complete octets on all atoms. The reasonable Lewis structure for SO_2 has one sulfur-oxygen single bond and one sulfur-oxygen double bond, with lone pairs arranged to minimize formal charges, matching the structure: O–S=O with two lone pairs on each oxygen and one lone pair on sulfur.