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

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

Step-by-step 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.