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difference between Valence bond theory and molecular orbital theory?


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#1 mahela007

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Posted 1 September 2009 - 06:49 AM

What is the difference between VB theory and Molecular orbital theory?
Tutorials on valence bond theory state that the orbitals of the individual atoms overlap when a bond forms. Doesn't that also form a molecular orbital?
if so what is molecular orbital theory?
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#2 hermanntrude

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Posted 1 September 2009 - 10:22 AM

in VB theory, the overlapped orbitals are usually only two orbitals and they closely resemble the orbitals they are made from. No mention is made of anti- or non- bonding orbitals in VB theory, and no mathematical attempt is made to actually define the resultant orbitals. In MO theory, however, the MOs are calculated precisely to give new orbitals, usually in pairs of anti-bonding and bonding orbitals. Also several orbitals can be combined to form several MOs (think of the MOs for benzene... valence bond doesn't come close to that).

because of that, MO theory can predict several things that VB theory can't, such as magnetism, precise bond order and aromaticity
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#3 tomy

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Posted 3 September 2009 - 05:56 AM

VBT just explain the hybridization only at rare levels.but MOT clearly explains bonding MO's anti bonding MO's.Thats why it has more advantages on VBT.
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#4 John Cuthber

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Posted 3 September 2009 - 05:42 PM

One important difference is that I can do the "maths" for VB theory in my head.
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