Which of the following statements correctly describes the Lewis dot structure of the formate ion, HCO2-?

• A. It contains a triple bond between carbon and one oxygen atom.
• B. It has no resonance structures and the negative charge is located on the hydrogen atom.
• C. It contains two equivalent resonance structures, each with a double bond between carbon and one oxygen, and a single bond between carbon and the other oxygen.
• D. It has a single resonance structure with both oxygens bonded to carbon by single bonds.

Answer: (C)

Verified step by step guidance

1. Step 1: Identify the atoms and total valence electrons in the formate ion (HCO2-). Carbon has 4 valence electrons, each oxygen has 6, hydrogen has 1, and the negative charge adds 1 extra electron. Sum these to find the total number of valence electrons to be used in the Lewis structure.
2. Step 2: Arrange the atoms with carbon as the central atom bonded to the two oxygen atoms and the hydrogen atom bonded to carbon. This is because carbon typically forms four bonds and is less electronegative than oxygen.
3. Step 3: Draw single bonds between carbon and each oxygen, and between carbon and hydrogen. Then distribute the remaining electrons to satisfy the octet rule for oxygen atoms and carbon, keeping in mind the total valence electrons calculated.
4. Step 4: Check for resonance by seeing if the double bond can be placed between carbon and either oxygen atom. Since the negative charge can be delocalized, draw two resonance structures where the double bond alternates between the two oxygens, making them equivalent.
5. Step 5: Confirm that the resonance structures show equivalent bonding with one double bond and one single bond to oxygen in each structure, and that the negative charge is delocalized over the oxygen atoms, not on hydrogen.