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I have understood the formation of $\ce{CH4}$ by valance bond theory, but I'm having trouble understanding it through molecular orbital theory.

The energy level diagram of molecular orbitals of $\ce{CH4}$ is not clear to me.

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closed as unclear what you're asking by airhuff, Klaus-Dieter Warzecha, M.A.R., Jan, Jon Custer Apr 4 '17 at 13:07

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    $\begingroup$ What specifically are you having trouble with? $\endgroup$ – bon Apr 19 '16 at 20:57
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Methane doesn't illustrate the difference very well, but the difference is nicely illustrated with benzene. Valence bond theory would have the electrons in the "double bonds" isolated between atoms as so:

enter image description here

But the electrons in the "double bonds" are not isolated in three double bonds but distributed equally over all 6 carbon atoms. Valence bond theory tries to wiggle out of this dilemma by posing the Kekule resonance structure:

enter image description here

which still belies the situation. The double bonds don't "resonate." The extra 6 electrons are distributed in one aromatic molecular bond (with three degenerate orbitals) evenly over the 6 carbon atoms.

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    $\begingroup$ Did you read the question? The OP wasn't asking about the different approaches that MO and VB theory take to double bonds. $\endgroup$ – KanyeBest Apr 19 '16 at 21:15
  • $\begingroup$ I've edited the question to try to point out the difference better. I don't really think the OP wants to know why MO and VB theory give difference values for the bonding energies when you crunch the numbers. I think the OP is missing the idea that VB theory isolates chemical bonds as only being between two particular atoms. To me this problem is best illustrated with conjugated double bonds. $\endgroup$ – MaxW Apr 19 '16 at 21:20
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    $\begingroup$ @MaxW The bonds in $\ce{CH4}$ are not conjugated, though. $\endgroup$ – ringo Apr 19 '16 at 21:27
  • $\begingroup$ @Ringo - I know that methane doesn't have conjugated bonds but I'm trying to show why VB isn't enough and why MO are more general. The difference between the two in methane just seems much much harder to explain. I don't see how you'd explain the difference without crunching the numbers which is very complex. $\endgroup$ – MaxW Apr 19 '16 at 21:32
  • $\begingroup$ There is an explanation in this weblink that directly answers the question, but I really don't think that it will solve the OP's dilemma. users.csbsju.edu/~frioux/h2bond/MethaneMOBonding.pdf // I really should have waited for the OP to clarify bon's query about what wasn't understood rather than guessing... $\endgroup$ – MaxW Apr 19 '16 at 21:37

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