Energy differences of molecular orbitals

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The discussion centers on comparing the energy levels of molecular orbitals, specifically the 1s antibonding orbital and the 2s bonding orbital in molecules A-A and A-B. It is established that antibonding orbitals are generally higher in energy than bonding orbitals. The construction of molecular orbital (MO) diagrams is emphasized, with the skill being taught in inorganic chemistry courses. A point of confusion arises regarding the energy levels, with one participant initially asserting that the 1s antibonding orbital is higher in energy than the 2s bonding orbital. However, this claim is later corrected, referencing a textbook that states for homonuclear diatomic molecules from hydrogen to neon, the 2s-2s bonding orbitals are indeed higher in energy than the 1s-1s antibonding orbitals.
Helena Wells
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Suppose we have a molecule A-A and a molecule A-B . And we want to compare the differences in energy of the different molecular orbitals for example the 1s antibonding orbital with the 2s bonding orbital.How can we do that?
 
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Antibonding orbitals are higher in energy than bonding orbitals. you can construct MO diagrams by following certain rules. at my university the skill is taught in inorganic chemistry
 
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docnet said:
Antibonding orbitals are higher in energy than bonding orbitals. you can construct MO diagrams by following certain rules. at my university the skill is taught in inorganic chemistry
I don't think that is true . Are you saying the 1s antibonding orbital has higher energy than the 2s bonding orbital?
 
Helena Wells said:
I don't think that is true . Are you saying the 1s antibonding orbital has higher energy than the 2s bonding orbital?
I was mistaken. Now I don't think the question makes any sense.
 
Here you go. My textbook says 2s-2s bonding orbitals are higher in energy than the 1s-1s antibonding orbitals for homonuclear diatomiicc molecules of the first 10 elements, from H to Ne.
Screen Shot 2021-02-21 at 5.52.43 PM.png
 

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