Half filled and completely filled orbital have extra stability why?
Answers
Answer:
Why are half filled and fully filled orbitals more stable than partially filled orbitals?
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I assume you’re asking this because of some unusual electron configurations you’ve encountered, so I’m gonna go ahead and disagree with pretty much all the other answers and tell you that half and fully filled orbitals aren’t more stable (at least practically). This is a big myth that has been perpetuated to explain the anomalous electron configurations of some of the transitions metals. Usually, Cr and Cu are given as examples since their configurations are [Ar]4s13d5 and [Ar]4s13d10 instead of the “predicted” [Ar]4s23d4 and [Ar]4s23d9 . People usually leave out elements like niobium, ruthenium and rhodium which also have weird configurations but not half or full shells ( [Kr]5s14d4 , [Kr]5s14d7 and [Kr]5s14d8 ).
You’ll also not see this trend in the p-shell and if you look at a graph of ionization energies you’ll find that the p3 and p6 columns are right on their expected trend lines, no noticeable extra stabilization. You should also note that the p4 column is, predictably, lower than the p3 because of the added coulombic repulsion from electron pairing. Electron pairing energies are the real culprits in many of the anomalous configurations.For chromium, it turns out the 4s and 3d orbitals are virtually degenerate. This means that the energy required to pair two electrons in the 4s orbital is more than the energy required to move up and put an electron in the 3d orbital. No need to invoke electron exchange energy here. For Cu, the 3d orbital is simply lower in energy than the 4s and lower than the pairing energy so it fills up first. The problem is that each atom needs to be considered independently. The electronic structure and therefore order of the orbitals isn’t completely fixed, it varies from atom to atom so it’s much easier to invoke this “half filled or fully filled” myth to explain things.
I’ll add that I don’t think symmetry plays any part here. However, exchange correlation energy is stabilizing, as some of the other answers have said, but in most cases it has a negligible effect. All it really tells us is that unpaired electrons should have the same spin.