What are the molecular orbital configurations for N+2, N2+2, N2, N−2, and N2−2?

1 Answer
Truong-Son N.
Nov 2, 2015

If we build the MO diagram for N2, it looks like this:

![www.ch.ic.ac.uk)

First though, notice that the p orbitals are supposed to be degenerate. They weren't drawn that way on this diagram, but they should be. Anyways, for the electron configurations, you would use a notation like the above.

g means "gerade", or even symmetry upon inversion, and u means "ungerade", or odd symmetry upon inversion. It's not crucial that you memorize which ones are gerade and which ones are ungerade, because the πg are antibonding, yet the σu are also antibonding, for example.

That is why I will use the easier notation to understand---the * notation. In here, σ* and π* are both antibonding. However, I will provide both if you want to compare.

If we write the configurations, they look like this:

N2:

[core 1s]2(1σg)2(1σu)2(πxu)2(πyu)2(2σg)2(πxg)0(πyg)0(2σu)0

or

[core 1s]2(σ2s)2(σ*2s)2(π2px)2(π2py)2(σ2pz)2(π*2px)0(π*2py)0(σ*2pz)0

The red labels indicate that they are empty for neutral N2 and you do not have to write them out.

Then if you want to do it for the ions, you just take out or add in electrons to the red-labeled configuration portions. Again, I will use the * notation because I find it easier to remember which MOs are antibonding/bonding.

N+2:

[core 1s]2(σ2s)2(σ*2s)2(π2px)2(π2py)2(σ2pz)1(π*2px)0(π*2py)0(σ*2pz)0

N2+2:

[core 1s]2(σ2s)2(σ*2s)2(π2px)2(π2py)2(σ2pz)0(π*2px)0(π*2py)0(σ*2pz)0

N−2:

[core 1s]2(σ2s)2(σ*2s)2(π2px)2(π2py)2(σ2pz)2(π*2px)1(π*2py)0(σ*2pz)0

N2−2:

[core 1s]2(σ2s)2(σ*2s)2(π2px)2(π2py)2(σ2pz)2(π*2px)1(π*2py)1(σ*2pz)0

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