Outer valence electrons for d-block elements (Se to Zn)

[Salman2]

I wish to better understand the configuration situation for the outer most valence electrons for the d-block elements, Sc to Zn.

I am having a problem understanding how to predict where the two outer most valence electrons must be located for some of the ten d-block elements? For some elements it seems to be clear, such as for the first three Se, Ti and V, where the outer most valence electrons are expected to be in the higher energy 4s sub shell, where they are paired with opposite spin $\uparrow$$\downarrow$ in 4s.

But, where are the two outer most electrons predicted to be located for Cr and Cu, given that both have a 4s1 configuration with a single spin up $\uparrow$ electron ? Are both valence electrons in the lower energy 3d for these two elements, or does one electron come from 4s and one from 3d ?

Also, what is the current status of Ni ? On Wiki a claim is made, with book reference, that Ni has a [Ar]3d9, 4s1 configuration for ground energy state, yet almost all chemistry texts use [Ar]3d8,4s2 for Ni.

So, if the 4s1 is correct based on energy calculations, I have the same question as above, would the two valence electrons for Ni come from 3d, or one from 4s and one 3d ? And, if from 3d, are they the two spin up $\uparrow$ electrons, or one of the $\uparrow$$\downarrow$ pairs found in 3d ?

Conversely, if 4s2 is the correct ground energy case for Ni, does that mean the two valence electrons come from 4s as $\uparrow$$\downarrow$, as is found in Sc and Ti and V ?

Then, is it possible that for Ni the quantum situation is that BOTH [Ar]3d9,4s1 AND [Ar]3d8,4s2 are quantum electron configuration possibilities, and if yes, how would quantum theory explain this ?

Which raises a final question, has the electron configuration been experimentally tested for each of the five stable Ni isotopes separately using ultra-pure samples of Ni-64, Ni-62, Ni-61, Ni-60, Ni-58, all of which are available commercially for sale ? I realize no difference is expected in electron configuration between the five stable isotopes of Ni, but, have the experiments been conducted on each isotope in ultra-pure state separately to rule out the possibility that some difference may be present? I ask because it is known that superconductivity effects can differ between isotopes of the same element, could such isotope effects be present in some of the d-block elements for electron configuration?...just asking.

Thanks for any help with the confusing d-block situation for electron configuration.

 

[Borek]

You are not going to like this answer... Don't bother. Thing is, energy differences between these configurations are very small, often below accuracy of our experiments and calculations, so it is very hard to find the conclusive answer.

You already know the general trend, and you know sometimes it gets broken. The differences you are talking about are of a low practical importance. Yes, there are people who will discuss them to death. Not much better than discussing number of angels on the pinhead if you ask me.

 

[Salman2]

When you say the energy differences are very small between 3d and 4s orbitals, are they really much smaller than the differences between the 2s and 2p orbitals where the general trend of Hund's Rule works well ? So, why not look for a replacement to Hund's Rule, a rule that does not get broken for d-block elements ? For example, suppose electrons for d-block elements have a closer affinity to protons than Hund's Rule predicts, and once we understand this, the new knowledge opens practical applications of d-block elements we now have no idea exists ? I do appreciate your reply, does not seem that anyone else has an interest in the topic.

 

[Borek]

Hund's rule is an experimental observation - simple, works for most cases, is not guaranteed to work always. I doubt you will be able to find something similarly simple and covering so wast number of cases.

In general we don't need another rule - we do know enough to calculate most of the things we need using much more rigorous methods. Yes, they still fail sometimes, but it is quite unlikely that we miss something big - more like we have technical problem with solving the equations.

 

[Einstein Mcfly]

This is an "issue" only insofar as we need to have the periodic table match up with atomic spectroscopy experiments using the simple orbital approach. This issue doesn't arise if you look at the electron configurations of atoms in solution. Those are just fine. It's gas phase atoms and their ionization potentials (which aren't that relevant to chemistry) that are the issue.

Take a look at:
J. Chem. Educ., 1996, 73 (7), p 617
and/or
Transition Metal Configurations and Limitations of the Orbital Approximation
Volume 66 Number 6 June 1989 481
or
http://ericscerri.blogspot.com/
Scerri writes a lot about this in J. Chem. Ed and elsewhere.