bond order

[ssh18]

I am still confused about bond order. Some places I read that it's the number of bonds between 2 atoms whereas others it says it's 1/2 (BO-AB)

How do I figure out bond order? Also, this might be really silly but He2 doesn't exist as a molecule right? Helium gas is He?

Thanks!

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[chemnerd31]

Both are okay. If you draw out the molecular orbital diagram for oxygen (O2) for example you will see that there are 8 bonding electrons and 4 antibonding electrons you would then divide this by two since there are two electrons per bond to get a bond order of 2. If you draw out a proper lewis structure for O2 you come to the same conclusion by counting number of bonds. Being an inorganic chemistry I personally like the molecular orbitals but either will work for the MCAT

 

[ssh18]

Hi - thanks! I'm sure I'm missing something but when I draw out the lewis structure for O2, there are 4 bonding electrons right (double bonds between the O's). In that case, isn't it 1/2(4-4)?? that's why I'm confused. I'm sure I'm missing something here.

 

[chemnerd31]

When you draw out the lewis structure for O2 you should notice that a double bond holds the oxygens together therefore it has a bond order of 2. In the case of a lewis structure look at the number of bonds between the atoms to determine bond order (this is of course neglecting things that have resonance structures). Or you could say there are 4 electrons in the bond and 4/2 is 2.

 

[justpremed]

i'm not sure how you're getting 1/2 (4-4)...are you confusing anti-bonding and non-bonding electrons?

 

[Chemist0157]

That's what it looks like to me.

 

[ssh18]

Thanks guys! I kept thinking that the formula was 1/2(#of bonding e - #of nonbonding e) but it's anti-bonding e and not lone pairs