Question

Which of these molecules and polyatomic ions cannot be adequately described using a single Lewis structure? Check all that apply.
CO3 2-

COH2

HCN

O3

NH4+

OF2

Answer 1

Answer:

$CO_3^-^2$ , $COH_2$, $HCN$, $O_3$

Explanation:

In figure 1 we can several structures for $CO_3^-^2$ in which the double bond can be moved across the oxygens due to the resonance.

In figure 2 the double bond between the carbon and the oxygen in $COH_2$ can be delocalized to the oxygen generating a new lewis structure in which we have a negative charge in the oxygen and a positive charge in the carbon.

In figure 3 we have again a delocalization process upon the nitrogen in order to produce a negative charge in the nitrogen and a positive charge in the carbon generating a new lewis structure.

In figure 4 due to the resonance, the double bond to the central oxygen can be moved from left to right generating 2 lewis structures.

Finally in the two last molecules is not possible to move the electrons. For $NH_4$ is not possible because there are no electrons to move. In the case of $OF_2$ the movement of electrons would generate structures too unstable so it is not possible to generate more lewis structures.