Which of the following is the correct Lewis structure for the formate ion, CHO2-, including its formal charges?

• A. A central carbon atom double-bonded to both oxygens and single-bonded to a hydrogen atom.
• B. A central carbon atom single-bonded to two oxygens (each with a negative charge) and single-bonded to a hydrogen atom.
• C. A central carbon atom single-bonded to a hydrogen atom and triple-bonded to one oxygen atom.
• D. A central carbon atom double-bonded to one oxygen, single-bonded to another oxygen (with a negative charge), and single-bonded to a hydrogen atom.

Answer: (D)

Verified step by step guidance

1. Step 1: Determine the total number of valence electrons for the formate ion (CHO2-). Carbon has 4 valence electrons, hydrogen has 1, each oxygen has 6, and the negative charge adds 1 extra electron. So, total valence electrons = 4 + 1 + (2 × 6) + 1 = 18 electrons.
2. Step 2: Arrange the atoms with carbon as the central atom, since it is less electronegative than oxygen. Connect the carbon to the hydrogen and both oxygens with single bonds initially.
3. Step 3: Distribute the remaining electrons to satisfy the octet rule for the oxygen atoms first, placing lone pairs on oxygens to complete their octets. Remember that hydrogen only needs 2 electrons.
4. Step 4: To minimize formal charges, form a double bond between the carbon and one oxygen atom. 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: Confirm that the Lewis structure has the lowest possible formal charges, with the negative charge localized on the single-bonded oxygen, and that the carbon has no formal charge, matching the correct structure described.