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MO theory, bond order and diatomic energy level diagrams

I've just finished (finally) drawing an energy level diagram for O2, but now I have to find the bond order for a superoxide ion....I know it has 13 valence electrons as opposed to 12 for O2, but I don't understand where i would put it on the energy level diagram? How would I know where it would go??

I found the answer, b.o=1/2(8-5)= 1.5 and i know that O2 is b.o=1/2(8-4)=2, but i dont understand why it wouldnt be 9-4 instead of 8-5?

Sorry if I didn't explain it very well! Any help would be appreciated :smile:

Reply 1

EierVonSatan

The extra electron would go in the LUMO, for ³O₂ this would be in the pi^* orbitals which is antibonding :smile:

O₂ should be = 1/2 (10 - 6) = 2

So O₂^- = 1/2(10 - 7) = 1.5

Reply 2

nikki14

Thank you! Just a couple of questions, sorry for sounding ignorant, but what is the LUMO? In my book it says O2 is 1/2(8-4), how did you get 10-6? Are you including the 1s electrons?

Reply 3

EierVonSatan

Lowest unoccupied MO :smile:

I am counting the 1s electrons, yes (so should your book :p:

)

Reply 4

nikki14

Ahhh, so thats a general rule..so a peroxide ion has 2 extra electrons (than O2) so the 2 electrons would go to the LUMO and the bond order would be 1/2(8-6)?

Haha this is a brand new university issued textbook so it definitely should! I assume as it doesn't I wouldn't have to in an exam...hopefully!

Reply 5

sunit sinha

Original post by nikki14

Thank you! Just a couple of questions, sorry for sounding ignorant, but what is the LUMO? In my book it says O2 is 1/2(8-4), how did you get 10-6? Are you including the 1s electrons?

yes 1s is also included

Reply 6

charco

Study Forum Helper

Original post by sunit sinha

yes 1s is also included

I am sure that Nikki14 appreciates your help after his/her question of six and a half years ago!...

... particularly as EVS actually answered the question seven minutes later ...