Which of the following best describes the correct Lewis dot structure for the neutral compound H2CO (formaldehyde)?

• A. The carbon atom forms a triple bond with oxygen and single bonds with each hydrogen; oxygen has one lone pair.
• B. The carbon atom forms a double bond with oxygen and single bonds with each hydrogen; oxygen has two lone pairs.
• C. The carbon atom forms single bonds with both oxygen and hydrogen atoms; oxygen has three lone pairs.
• D. The carbon atom forms single bonds with each hydrogen and no bond with oxygen; oxygen has four lone pairs.

Answer: (B)

Verified step by step guidance

1. Step 1: Determine the total number of valence electrons in the molecule H2CO. Hydrogen has 1 valence electron each, carbon has 4, and oxygen has 6. Add these together to find the total valence electrons available for bonding.
2. Step 2: Identify the central atom, which is usually the least electronegative atom that can form multiple bonds. In H2CO, carbon is the central atom, with hydrogen and oxygen bonded to it.
3. Step 3: Arrange the atoms with carbon in the center, single bonds connecting carbon to each hydrogen, and a bond between carbon and oxygen. Then, distribute the remaining valence electrons to satisfy the octet rule for carbon and oxygen, placing lone pairs on oxygen as needed.
4. Step 4: Consider the bonding between carbon and oxygen. Since carbon needs to complete its octet and oxygen also prefers an octet, a double bond between carbon and oxygen is typically formed. This allows carbon to have four bonds total (two single bonds to hydrogens and one double bond to oxygen).
5. Step 5: Confirm the number of lone pairs on oxygen. After forming a double bond with carbon, oxygen will have two lone pairs to complete its octet. This matches the correct Lewis structure where carbon forms a double bond with oxygen and single bonds with each hydrogen, and oxygen has two lone pairs.