Consider the formate ion, HCO₂^-, which is the anion formed when formic acid loses an H⁺ ion. The H and the two O atoms are bonded to the central C atom. (c) Would you predict that the C—O bond lengths in the formate ion would be longer or shorter relative to those in CO₂?

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1. Identify the type of bonds present in both the formate ion (HCO2-) and carbon dioxide (CO2). In CO2, each carbon-oxygen bond is a double bond (C=O). In the formate ion, resonance structures suggest a bond order between a single and a double bond for the C-O bonds.
2. Understand the concept of resonance in the formate ion. The formate ion can be represented by two resonance structures, where the negative charge is delocalized between the two oxygen atoms. This delocalization results in a bond order that is an average of a single and a double bond.
3. Compare the bond orders. In CO2, the bond order is 2 (double bond), while in the formate ion, the bond order is approximately 1.5 due to resonance.
4. Relate bond order to bond length. Generally, a higher bond order corresponds to a shorter bond length because more electron density between the atoms pulls them closer together.
5. Predict the bond length. Since the bond order in the formate ion is lower than in CO2, the C-O bond lengths in the formate ion are expected to be longer than those in CO2.