What is the bond order of the C→O bonds in the acetate ion?
The Correct Answer and Explanation is :
To determine the bond order of the C→O bonds in the acetate ion (C₂H₃O₂⁻), we need to consider its Lewis structure and the concept of bond order. The acetate ion has two resonance structures, which contribute to its overall stability and the characteristics of the C→O bonds.
Lewis Structure and Resonance
The acetate ion can be represented by two primary resonance structures:
- Structure 1: In this structure, one carbon-oxygen bond (C=O) is a double bond, while the other carbon-oxygen bond (C-O) is a single bond. The structure also has a negative charge on the oxygen atom that is single-bonded to carbon.
- Structure 2: This is a mirror image of Structure 1, where the double bond shifts to the other oxygen atom, and the negative charge is transferred to the opposite oxygen.
Bond Order Calculation
The bond order is defined as the number of bonding pairs of electrons between two atoms divided by the number of bond segments between them. In the case of the acetate ion:
- Each resonance structure contributes to the overall electron density between the carbon and oxygen atoms.
- In the resonance hybrid of acetate, the carbon atom is effectively bonded to two oxygen atoms: one with a double bond (C=O) and one with a single bond (C-O). However, due to resonance, the character of these bonds is a blend of single and double bonds.
To calculate the bond order for each C→O bond in the acetate ion:
- In the resonance hybrid, each C→O bond can be considered as having a bond order of ( \frac{1 \text{ (from the C=O bond)} + 1 \text{ (from the C-O bond)}}{2} = 1.5 ).
Conclusion
Thus, the bond order for each C→O bond in the acetate ion is 1.5. This value indicates that the bonds are stronger than a single bond but not quite as strong as a double bond, reflecting the delocalization of electrons due to resonance. The bond order of 1.5 also explains the stability and reactivity of the acetate ion in various chemical reactions.