According to moleculaer orbital theory predict the bond order for N2?

Question

a) 1

b) 2

c) 2.5

d) 3

e) 3.5

I know the answer is 3 but why? please explain will give 5 pts for best answer thanks

Answer 1

It is 3 because your three 2p orbitals on each nitrogen combine to give a total of six p-based molecular orbitals.  They are a sigma bonding orbital (two pz orbitals collide head-on), and a matching sigma antibonding orbital (these are at the very bottom and very top of the energy diagram, respectively), plus two pi bonding orbitals (two px orbitals interact side-on, two py orbitals interact side-on) with two matching pi antibonding orbitals.  

They look like this

___ sigma antibonding

___  ___  pi antibonding

___  ___  pi bonding

___ sigma bonding

Because nitrogen has 3 p electrons, you use six total electrons to fill in this diagram.  You will fill in all three of the bonding orbitals (hence the bond order of 3) but none of the antibonding orbitals.