How do I calculate the bond order for H2- and H2+?

1 Answer
Truong-Son N.
Apr 1, 2017

I'm assuming you mean #"H"_2^(-)# vs. #"H"_2^(+)#. Well, build the molecular orbital (MO) diagram. Each hydrogen atom contributes one electron, and thus, #"H"_2^(-)# has three electrons while #"H"_2^(+)# has one.

Each hydrogen atom contributes one #1s# atomic orbital, and thus, the orbitals overlap according to MO theory to form one #sigma_(1s)# and one #sigma_(1s)^"*"# MO by conservation of orbitals.

If you calculate their bond order, you get:

#"BO"_(H_2^(+)) = 1/2("Bonding" - "Antibonding")#

#= 1/2(1-0) = 1/2#

#"BO"_(H_2^(-)) = 1/2("Bonding" - "Antibonding")#

#= 1/2(2-1) = 1/2#

So, neither is more stable than the other. But of course, they are less stable than #"H"_2#. What does bond order mean in terms of bond strength?

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