[jamesmith134]

Hello,

I wanted to know if we are talking about the Molecular Orbital, do you consider all the electrons of the atom to be part of the Molecular orbital, or just the valence electrons?

For example, if I am given the molecule N₂ and I am asked about how many electrons are in the molecular orbitals, is it 10 ? (5 + 5 valence electrons) or the total of 7 + 7 = 14?

Thanks

[Corribus]

In general we approximate the molecular orbitals as only being formed from combinations (usually pairs) of the valence orbitals, because overlap of non-valence orbitals is extremely small and energetic separation between valence and non-valence orbitals is very large. More sophisticated calculations include all orbitals that have the appropriate symmetry and can therefore participate in bonding models. Inclusion of such terms attenuates the eigenvalues to some degree, but using a valence-only approach is a reasonable approximation for many purposes.

[Corribus]

(EDIT of previous post: when I said "usually pairs", I meant for diatomics. Molecules with more nuclei have more valence atomic orbitals that are combined to form molecular orbitals. E.g., in benzene, the pi-molecular orbitals are formed using six atomic valence 2pz orbitals of the six carbon centers.)