Do the molecular orbitals that are occupied by electrons have MORE or LESS nodes than the unoccupied orbitals, and are they at a HIGHER or LOWER energy level?

Question

A) A molecule with eight carbons and alternating single and double bonds (C=C-C=C-C=C-C=C) has eight delocalized electrons in large molecular orbitals that span the length of the molecule. Eight atomic p orbitals from the carbons overlap to form HOW MANY molecular orbitals?

b. Do the molecular orbitals that are occupied by electrons have MORE or LESS nodes than the unoccupied orbitals, and are they at a HIGHER or LOWER energy level?

Answer 1

Hi Arianna W.,

Just like on a single atom, the less-noded orbitals are occupied first. And, just like on an atom, each orbital can only take 2 electrons. So that means that 4 molecular orbitals are used. You can easily discern the signing for the lowest energy one, it has one (in-plane) node, so the wave function is let's say + on the top and - underneath, and it extends across all 8 atoms. The next level up has also one vertical node, right in the middle, and you can probably take it from there? And always, the largest orbitals (even as pieces!) are lowest energy -- electron like their elbow room!

-- Cheers, --Mr. d.