[NewtoAtoms]

Hello,

can anyone explain to me why N2 has an interatomic distance of 0.112 nm and N2+ has an interatomic distance of 0.129 nm

BUT

Cl2 has an interatomic distance of 0.199 whereas Cl2+ has an interatomic distance of 0.189??

Thank you!!

[Yggdrasil]

To answer this question, you will need to draw out the molecular orbital diagrams for N₂ and Cl₂ and consider the effect of removing an electron on the bond order.

[NewtoAtoms]

Hello Yggdrasil,

I have drawn out the molecular orbital diagrams for N2, N2+, Cl2, Cl2+

N2:      (σ1s)2(σ1s*)2(σ2s)2(σ2s*)2(π2py)2(π2pz)2(σ2px)2    0.112 nm
N2+:    (σ1s)2(σ1s*)2(σ2s)2(σ2s*)2(π2py)2(π2pz)2(σ2px)1    0.129 nm
Cl2:     (σ1s)2(σ1s*)2(σ2s)2(σ2s*)2(π2py)2(π2pz)2(σ2px)2(π2py*)2(σ2pz*)2  0.199 nm
Cl2+:   (σ1s)2(σ1s*)2(σ2s)2(σ2s*)2(π2py)2(π2pz)2(σ2px)2(π2py*)2(σ2pz*)1  0.189 nm

From this I can tell that N2+ will be longer because it has an unpaired electron in the (σ2px) orbital. 

However Cl2, and Cl2+ are backwards reasoning.

Because I would think that Cl2+ would be longer (similar to N2+) because it has a lone electron in (σ2pz*) orbitals... however the length of the Cl2 bond is 0.199 nm where as the bond length in Cl2+ is 0.189 nm SHORTER.

How can my text book be right?  How can that apply for bond length in N2 and N2+ but not Cl2 and Cl2+?
Can you suggest anything that would set me on the right path to understanding this?

Thank you for your help Yggdrasil!

New to Atoms

[Yggdrasil]

I don't think that having unpaired electrons has a major effect on bond lengths.  Instead, consider the concept of bond order:  http://en.wikipedia.org/wiki/Bond_order

[tamim83]

It is because of the orbital you are removing the electron from.  Removing an electron from a bonding orbital decreases the bond order and increases the bond length.  Removing an electron from an antibonding orbital increases the bond order and decreases the bond length.  So it depends on the type of orbital you are dealing with.