2C.3

[Ariel Davydov 1C]

Hi,

For part C of this question, I'm a little confused as to how there is resonance with the structure for HClO3. The structure you end up with (with the lowest formal charge) doesn't have any bonds that can be switched without changing the number of double/single bonds in the molecule, yet the answer key provides three structures with different formal charges on the elements in each molecule. Can someone explain how this is possible and if we will be tested on this?

I've attached a picture of the answer from the answer key to help explain my confusion a little more. Thanks!

[Angela Patel 2J]

I think the diagram is just pointing out that you can make the Cl formal charge 0 when there are two double bonds with oxygen.

[VPatankar_2L]

I think the answer key is saying that all three are possible resonance structures since Chlorine is in the third row of the period table and has an expanded octet. Thus, in the first diagram chlorine can have eight electrons surrounding in, in the second diagram Chlorine can have 10 electron, and in the third diagram Chlorine can have 12 electrons. But ultimately, the last diagram is the best structure because it has the lowest formal charge.