Exceptions to the Aufbau Principle

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Discussion Overview

The discussion centers around the exceptions to the Aufbau Principle in atomic theory, specifically questioning whether chromium and copper are the only exceptions and seeking a comprehensive list of such exceptions. The scope includes theoretical considerations and empirical observations related to atomic orbitals.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • One participant questions if chromium and copper are the only exceptions to the Aufbau Principle and seeks a complete list of exceptions.
  • Another participant suggests that based on experimental evidence, chromium and copper appear to be the only exceptions, implying that if there were others, they would likely be known.
  • A different viewpoint indicates that the identification of exceptions depends significantly on how the Aufbau Principle is defined and the methods used to determine atomic orbital energies.
  • Additional references to academic articles are provided, which may offer insights into the quantum mechanical explanations and empirical motivations for orbital configurations.
  • One participant explains that chromium and copper achieve stability by drawing an electron from the 4s orbital to fill or half-fill the 3d orbital, a phenomenon also observed in other elements within their groups.

Areas of Agreement / Disagreement

Participants express differing views on the number of exceptions to the Aufbau Principle, with some asserting that only chromium and copper are exceptions while others suggest that the definition of the principle may allow for more complexity. The discussion remains unresolved regarding the existence of additional exceptions.

Contextual Notes

The discussion highlights the dependence on definitions and methods for determining atomic orbital energies, which may influence the identification of exceptions to the Aufbau Principle. There is also mention of empirical evidence that supports the claims made.

smaan
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Are chromium and copper the only exceptions to the Aufbau Principle? If not, what are all the exceptions? Is there a list of some sort that would state all the exceptions to the Aufbau
Principle?

Thank you.
 
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Upon quick examination of the periodic table, yes they seem to be the only exceptions But keep in mind this is an experimental fact and pretty much all the elements have been tested for the validity of principle for each of them, so if there were any other exceptions, they would probably been known by now! SO for now you can bank on these two exceptions without worrying about the rest, because at this point in time there don't seem to be any other ones!
 
The answer to that question depends to a large degree on the definition of the aufbau principle, i.e. on the method by which you determine the energies of the underlying atomic orbitals.
 
Try these:

How Good is the Quantum Mechanical Explanation of the Periodic Table?, Journal of Chemical Education, 75, 1384-1385, (1998)
Why the 4s Orbital Is Occupied before the 3d, Journal of Chemical Education, 73, 6, 498-503, (1996) (Co-authored with M. Melrose).

There's also an interesting article from JCE that I can't seem to find that's all about how to empirically motivate orbitals from ionization potentials. That'll also be of interest to you.
 
They (Cr and Cu) draws one electron from 4s orbital to get half filled/fully filled 3d orbital, granting them pseudo-inert configuration, thus stabilizing them. This phenomena is shown by other members of their respective groups like (Cr, Mo) and (Cu, Ag, Au).
 

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