Okay, hopefully I've got this sorted in my head properly. We're looking at the d-block transition elements in particular, which have five outer (d) orbitals, with a total of 10 possible electrons. And there is a long explanation about the relative orientation of different orbitals and how they therefore interact in complexes, but basically there's two different energy levels among the d orbitals, like so:
So, say you have 1 d electron. It would probably go in the lower energy orbital: but it you were to increase its energy, via a light wave or something, it would go into the higher energy state: . But it's the same electron, with the same spin. Thus, this is a "Spin-Allowed Transition." (Wheras if I were designing chemistry, I would give such things much more, er, imaginative names, and all chem students would hate me...)
Okay, but say you have five d electrons (and the complex would rather fill the higher energy orbitals than deal with the energies between paired electrons):
If you were to fire some photons at this one, increasing the energy, you would expect one of the electrons in the lower orbitals to move into the higher orbitals, right? But, all the electrons have the same spin state (as per some orbital filling rule we covered last year that I can't remember right now) and we know there can't be two electrons with the same spin state in the same orbital, so this is a "Spin-Forbidden Transition."
At this point my prof got a strange smile, and explained that just because something is forbidden doesn't mean its not going to happen. It just isn't going to happen very often (and only, you see, when the electrons think they can get away with it). It doesn't happen all that often, but given how many electrons and molecules are in stuff, it happens often enough.
Now, I might have mislead you a little, because I didn't think everybody would have appreciated this whole explanation when I might have simplified into a sentence. There can't be two electrons in a given orbital, for reasons we're going to (I hope) gloss over in quantum mechanics, so what really happens is one of them flips spin: . (And there are other particular parallels that can be that, non? )
Now, see, I was sitting through this in lecture form, and somehow saw the dirty bits. I'm not sure that's right. (And will not subject the world to doomed-romance-between-electrons-until-one-of-them-undergoes-a-spin-change-operation-so-that-the-world-will-let-them-be-together fic things. Be glad.)
no subject
Okay, hopefully I've got this sorted in my head properly.
We're looking at the d-block transition elements in particular, which have five outer (d) orbitals, with a total of 10 possible electrons. And there is a long explanation about the relative orientation of different orbitals and how they therefore interact in complexes, but basically there's two different energy levels among the d orbitals, like so:
So, say you have 1 d electron. It would probably go in the lower energy orbital:
Okay, but say you have five d electrons (and the complex would rather fill the higher energy orbitals than deal with the energies between paired electrons):
If you were to fire some photons at this one, increasing the energy, you would expect one of the electrons in the lower orbitals to move into the higher orbitals, right? But, all the electrons have the same spin state (as per some orbital filling rule we covered last year that I can't remember right now) and we know there can't be two electrons with the same spin state in the same orbital, so this is a "Spin-Forbidden Transition."
At this point my prof got a strange smile, and explained that just because something is forbidden doesn't mean its not going to happen. It just isn't going to happen very often (and only, you see, when the electrons think they can get away with it). It doesn't happen all that often, but given how many electrons and molecules are in stuff, it happens often enough.
Now, I might have mislead you a little, because I didn't think everybody would have appreciated this whole explanation when I might have simplified into a sentence. There can't be two electrons in a given orbital, for reasons we're going to (I hope) gloss over in quantum mechanics, so what really happens is one of them flips spin:
Now, see, I was sitting through this in lecture form, and somehow saw the dirty bits. I'm not sure that's right. (And will not subject the world to doomed-romance-between-electrons-until-one-of-them-undergoes-a-spin-change-operation-so-that-the-world-will-let-them-be-together fic things. Be glad.)