Do 3 electron bonds really exist?

[kichigai]

I read in Cotton & Winkinson that some bonds can have 3 electrons in them. HOw is this possible?

 

[employee #416]

I can give you an example, but no explanation. Sorry for not being sufficient in my response.

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The triple bond is present between the two carbon atoms. Each carbon has four valence electrons, so it is able to bond with four different atoms. Since each carbon is bonded to a hydrogen, and hydrogen only has one valence electron. You can make a double or triple bond between Carbon and Hydrogen (forgot which principle this was). So, since there are 4 extra electrons, two extra bonds form between the two carbons. This was not explained well, sorry.

 

[kichigai]

I can give you an example, but no explanation. Sorry for not being sufficient in my response.

H:C:::C<img src="/styles/physicsforums/xenforo/smilies/arghh.png" class="smilie" loading="lazy" alt=":H" title="Gah! :H" data-shortname=":H" />

The triple bond is present between the two carbon atoms. Each carbon has four valence electrons, so it is able to bond with four different atoms. Since each carbon is bonded to a hydrogen, and hydrogen only has one valence electron. You can make a double or triple bond between Carbon and Hydrogen (forgot which principle this was). So, since there are 4 extra electrons, two extra bonds form between the two carbons. This was not explained well, sorry.

Does this mean that the sigma bond has 3 electrons in it and that the pi bond has 3 electrons in it?

 

[employee #416]

Haha, it's been awhile since I've done bond structures. I haven't had chem since summer started. If I'm not mistaken the sigma bond is the primary bond between two atoms, and the pi bonds are the bonds after that. The sigma bond and pi bonds will have 2 electrons each. You have one sigma bond and two pi bonds. Thats 2+2+2=6 electrons which is a triple bond. I'm not sure if that is what you are looking for.

I see where you are getting that question from. I used semi-colons to show the pair of electrons. I should have used lines. You are reading them straight across. Read them up and down and you'll see there are two electrons a pair.

 

[kichigai]

Sorry 'bout that. Forgot to switch to my 3D goggles.
I am fishing for an answer that involves wave functions. Can you help with this?

 

[movies]

Wouldn't this just be a molecule with an electron occupying one of the anti-bonding orbitals? For example, ethylene with one of the pi electrons excited into the sigma star orbital of the sigma bond between the two carbons.

 

[Chemicalsuperfreak]

Perhaps you mean three-centered bonds?

Like H3+, where three atoms are bonded together with two electrons?

 

[Mike H]

Could the text that the OP cited simply be referring to the bookkeeping that is occasionally done in an average sense? For example, if one has a deprotonated carboxylic acid moiety where there's delocalization over the functional group? E.g., sometimes there's a double bond, sometimes there's a single bond, on the average there's a bond and a half...

 

[Ostwald]

kichigai... Where in Cotton and Wilkinson did you see that about three electron bonds?

 

[kichigai]

kichigai... Where in Cotton and Wilkinson did you see that about three electron bonds?

Ooops! The correct source is: Linus Pauling "The Nature of the Chemical Bond"
C&W only discuss electron deficient (1 electron) anomalies. Sorry!