Orbital sketch

Hi,
I need to provide an approximate sketch of the molecular orbitals formed in O2 and N2. Now I was wondering if you could look at the attached picture and just tell me if you agree with the way I sketched them.

Thanks a bunch, my exam is coming up so I really appreciate any comment!

mo.jpg353.7KB

Reply 1

Caperucitaroja

Note that the 1σg and 2σg in N2 are sp hybrid orbitals.

Reply 2

Sinuhe

They look fine for the most part; although I've never seen anyone mark bonding orbitals with a 'b' - were you taught to do this?

Another thing, in the dinitrogen case - the 1sigma_u and 2sigma_u orbitals should also be somewhat s-p mixed, and you shouldn't draw the orbital energy levels symmetrical with respect to 2s/2p orbitals due to this mixing. A good diagram is in the Valence lecture notes, p. 25 of the handout (or p. 3 in the file):
http://physchem.ox.ac.uk/~mb/teaching/vallectures56.pdf

Reply 3

Caperucitaroja

Thank you ! Those were really useful observations.

Yes, you are right about the energy levels not being symmetric, the bond MO is closer than the antibonding MO.
Do you reckon I should just not use the term b or * to indicate bonding and antibonding, is it enough with g and u?

Reply 4

Caperucitaroja

Sinuhe

They look fine for the most part; although I've never seen anyone mark bonding orbitals with a 'b' - were you taught to do this?

I actually think I started doing that after our tutorial. Not my tutor's fault though, he just suggested that since were were 'rookies' at MO theory we might label them b and * to aid our understanding, but now I do see it redundant so I will stop doing so.

Reply 5

Caperucitaroja

Alright, I corrected it, do you reckon this looks better? :smile:

mo2.jpg323.2KB

Reply 6

Sinuhe

That looks good now, yep. :smile:

I guess if you're used to it, it's fine if you want to include a 'b' - maybe just make a note of what it means in the exam? (What do you do for nonbonding orbitals then?)
It's quite common to include the star to indicate that an orbital is antibonding though, so you may want to keep doing that. But for simple symmetrical diatomics, the gerade/ungerade labels are certainly enough, so you don't *need* to include a star either if you don't feel like it.

But don't worry about this - I was just wondering why you used the 'b', as I hadn't ever seen it before. It's fine if you want to use it I should think! Probably makes it easier to specify the bond order anyway, doesn't it? :smile: