h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

If an isotope of a neutral atom were especially devoid of neutrons and therefore more 'skinny' or having a larger relative concentration of charge, would an electron be more likely to choose an inner orbital to be near the 'object of its desire' (the protons in the nucleus) even if that orbital was more convolute than it normally cared for?

Hmm... You don't really change much electronically by taking away some neutrons away from the nucleus. The charge is the same and in a first approximation it is coming from a very small source compared to the orbital's size. Additionally *all* orbitals would feel the change, so relatively to each other the energies would change even less... There is a change though (it can be measured) in the orbital's energy of different isotopes, but it's so faint it does not really interfere in the electronic characteristics. That is also the reason why it is so difficult to separate isotopes chemically. They are way more effectively separed due to the difference in mass. Their slightly different chemical behaviour can be attributed primarily to the change in mass and not the electronics (in fact, chemically they all behave the same, but heavier isotopes are sometimes slooower).

Hope that helped.

HELL

Whoa... Just read my scribblings again. Could be difficult to understand, sorry - maybe I should press the 'post message' button only after reading the post twice.

The answer to your question is: No - at least not for normal isotopes on this planet. On a plainly theoretical level this question is more difficult to answer, one would have to calculate the orbital's energies for these extreme cases (take some 100 neutrons away from Uranium - difficult). From what I know, I think that even in extreme theoretical cases the change on the orbital's relative energies would be so small that the answer would still be: No. If you go further and suggest neutron stars being considered as a nucleus - I don't know. I don't think anyone can calculate this one - at least not quantum mechanically.

Is this explanation better? Or even worse?

Anyways, thanks for reading the entry...

HELL

If there is a difference, it will show up in different spectra, but it may need a very high resolution of the spectrometer.

Oh yes Marijn (BTW: nice to see you around here) the difference can be seen (in the case of T,D and H it is quite big too, and the spin-orbit coupling is totally messy when you remove one or two neutrons from some heavier atoms, so spectroscopically you can see the different isotopes quite well) - The question was if the electron would take a different orbital - that is, if the order of the orbitals will change due to the different field gradient. And for that I think it would need too much difference in the field, which cannot ba achieved by removing even 10 or 20 neutrons from some heavy nuclei.

Bye,

HELL

Hmm.. I'll try again.

Isotopes:

a) Difference in couplings: YES, so detection by spectroscopy is quite easy.

b) Difference in quantum Numbers of the electron... Difficult to say. Heavy Atoms and outer shells have similar energies, so it *could* be that the filling order changes slightly. But I think it is quite improbable, because the difference of the field does not change too much after removing 1 or 2 neutrons from the nucleus.

(I think b was the first question of the thread)

Uff,

HELL

Hell,
I roamed some other parts of h2g2 the last couple of weeks, but I saw this entry as being overlooked. It probably isn't anymore.

I think the question can be answered from the spectra. You will have to reconstruct all energy levels from them, and then look if some levels changed places. If this happens, the filling order of those levels will change also.
Of course you also can try to solve the Schroedinger equations.

Empirical answers are always yummy. Thank you Marijn. And yes, I did understand what you were getting at, Hell, but the extra posts clarifying it were also welcome. Your entry was interesting, so I was happy to read it.

What is the major cause of an electron deciding that any particular orbital (say, the next orbital that a scientist who is fond of patterns would suppose it would occupy) is unsuitable?

Would knowing this help in synthesizing transuranic elements? I speculate that finding a more stable element than those currently synthesized might have an odd solution.

Oh no, the electrons have little to do with the synthesis of more stable heavy nuclei. The major problem is to get the nucleus stable and not the electron shells. And for that one has to analyse the nuclear wave-functions and not the electronic.

The major cause for an electron deciding that an orbital is unsuitable lies in the energy it will have in the particular orbital. If it finds one that is vacant with a lower energy it will get there. That's all. It has nothing to do with the calculations. In fact, sometimes electrons prefer stranger configurations than the one predicted in a first approximation (e.g. half shell and full shell configurations in the Lanthanoids). The reason for that is that certain energies are neglected in the rough first calculations (which work pretty well for the upper 3/4ths of the periodic table). If these contributions are included in the calculations everything fits.

When calculating very heavy atoms even 'stranger' contributions - which are perfectly negligible for lighter atoms . must be considered, like relativistic effects, in order to predict the exact energies of the electrons.

Cheers,

HELL