## Bond order of B2 molecule

Belicia Tang 1B
Posts: 32
Joined: Wed Sep 21, 2016 3:00 pm

### Bond order of B2 molecule

Hey guys,
So the bond order of B2 is equal to 1, which you can get by drawing the molecular orbital diagram and performing the equation Bond Order = .5 * (# of bonding electrons - # of antibonding electrons). However, when you draw the Lewis structure of B2, you get a triple bond. I always thought bond order corresponded to the number of bonds. That is, molecule held together by a single bond would have a bond order of 1, and a molecule held together by a double bond would have a bond order of 2, etc. Is B2 an exception to this rule?

Thanks!

EDIT: My mistake, B2 lewis structure is bounded by single bond. I don't know what I was thinking when I said triple bond, because the # of electrons don't even add up to 14. So the bond order of 1 is correct.
Last edited by Belicia Tang 1B on Fri Nov 11, 2016 12:36 pm, edited 1 time in total.

Jessie_Chen_2L
Posts: 20
Joined: Wed Sep 21, 2016 2:59 pm

### Re: Bond order of B2 molecule

The molecular orbital diagram for B2 is

You can see that there are two electrons in the σ 2s and two electrons in the σ*2s and two in the π 2p orbitals. We now know that there are two electrons in the antibonding orbitals and 4 in the bonding orbitals.

From this we can use the equation, Bond Order = 1/2(# of electrons in bonding orbitals - # of electrons in antibonding orbitals).

Bond Order = 1/2(4-2) = 1