Submitted by Sibrina Collins / Marburger STEM Center (MSC) at Lawrence Technological University on Fri, 11/19/2010 - 10:13
Forums

Dear Colleagues,

I hope all is well. Today, in my course I talked about the 18 electron-rule and gave the students a few problems to practice. I asked the students to determine if the complex Fe2(CO)9 followed the 18 electron rule. So, I go through the example and explain the the M-M bond contributes one electron. A student asked me "Where does the electron come from in the bond? Are you counting an electron twice from Fe?" I explained that I am not counting electron twice from Fe. What is the best way to explain this? I never had a student ask me where does the electron come from before. (Ha)  The formation of an M-M single bond provides an extra electron for each iron. Any thoughts on helping me explain this to an undergraduate?

Jim Goll / Edgewood College

I would say that the electron comes from the other iron atom.  It is shared just like  electrons in molecular hydrogen.  Sometimes you may also encounter a dative bond in a metal-metal bonded system that is a classic Lewis acid-base adduct.

Fri, 11/19/2010 - 10:38 Permalink
Sibrina Collins / Marburger STEM Center (MSC) at Lawrence Technological University
Thanks James! Sometimes we are asked the simplest questions, and we get stumped on how to respond!
Fri, 11/19/2010 - 10:45 Permalink
Sibrina Collins / Marburger STEM Center (MSC) at Lawrence Technological University

Chip,

That is certainly an interesting website!

SNC

Fri, 12/03/2010 - 20:18 Permalink
Sossi dishakjian / Lebanese University

I would say each iron atom provides one electron to form a metal-metal covalent bond, and like in counting number of electrons in a nitrongen atmn in a nitrogen molecule to see if N satisfies the octet, we count all the bonding electrons to belong to each of the bonded atoms.

Dr. Dishakjian

Wed, 01/05/2011 - 16:44 Permalink
Sibrina Collins / Marburger STEM Center (MSC) at Lawrence Technological University

Hi Sossi,

That's a good explaination as well.

SNC

Wed, 01/05/2011 - 21:52 Permalink