MO Diagram for C2+ and C2-

[Erica Harris 3H]

This is question 4A. from the 2010 final:

Which has a stronger bond? Give a reason:

C2+ or C2-

Can someone expand on the reasoning?

Thank you!

[saialam 1A]

The answer is C2- because of bond orders
When we draw the C2 MO, we have everything up till the PiPy Orbitlal filled, and the next orbital tht would be filled would be the sigma2Pz orbital.
As for bond orders it is 1/2*[(#e- in bonding orbitals)-(#e- in antibonding orbitals)]
Doing this, normally just C2 is 1/2*[(8)-4]=2
With C2-, we are adding an e- to the normal bonding shells so: 1/2*[(9)-4)]=2.5
And C2+, we remove one from the normal bonding shell so:1/2*[(7)-4)]=1.5
2.5>1.5 that is why the C2- is stronger.