Chapter 8, Problem 103A

Interpretation Introduction

Interpretation:

Resonance structure of ${\text{HCO}}_2^{-}$ needs to be explained.

Concept introduction:

A Resonance structure is the two or more correct Lewis structures which indicate a single molecule or ion. These structures differ only in electron pairs position. The location of atom is same in resonance structure.

Answer to Problem 103A

Two resonance structure of ${\text{HCO}}_2^{-}$are as follows:

Explanation of Solution

Resonance is a condition for those molecules which have more than one valid Lewis structure. The ${\text{HCO}}_2^{-}$

have two possible Lewis structure. In these structure only position of double bond and electron pairs are different. Valence electron of O is 6, C is four, hydrogen is 1 and one more electron due to negative charge. Total number of valence electron is 18. To complete octet, C forms a double bond with any of one oxygen atoms. Hence, the resonance structure is as follows:

The above two structure represents ${\text{HCO}}_2^{-}$ ion.

Conclusion

Each molecule or ion that undergoes resonance behaves as if it has only one structure.