# Talk:Electron configuration

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## Periodic Aufbar Image:FG08 03.jpg conversion

Discussed with others, and agree on the fact that image Image:FG08 03.jpg needs to be converted into HTML like normal periodic table.

## Stupid article or deliberate evil?!?

This whole article is written as if to confuse anyone who isn't a phd . It starts by giving no clear definition of s,p,d,f...It shows a picture of one element, then an explanation of another.. It's all deliberately made to be as confusing as possible. — Preceding unsigned comment added by 79.75.100.100 (talk) 22:54, 15 June 2016 (UTC)

## Discussions

One thing that is not clear is what the s, p, f, d names of the shells mean. Maybe someone can explain this.

Caruso 11:48, 3 November 2012 (UTC) — Preceding unsigned comment added by Carusus (talkcontribs)

This is explained in the section Notation, paragraph 4 which says (in part): The choice of letters originates from a now-obsolete system of categorizing spectral lines as "sharp", "principal", "diffuse" and "fundamental" (or "fine"), based on their observed fine structure: their modern usage indicates orbitals with an azimuthal quantum number, l, of 0, 1, 2 or 3 respectively. Dirac66 (talk) 17:47, 3 November 2012 (UTC)

I changed the notations for electron configuration to use the sup HTML tag instead of the math tag. I think it's easier to read (at least on my comp; please give feedback if you find it worse), as well as slightly easier to edit.

I added in a bit about how d subshells become more stable when half-filled or full, which results in configurations occasionally deviating from the table in the Aufbau section. Should this be noted as "Exception to the Aufbau principle" or "Exception to the aforementioned table"? Is the table the Aufbau principle itself or a general extrapolation?

Kurzon 11:41, 3 August 2005 (UTC)

I brought in information from the articles principal quantum number, azimuthal quantum number and magnetic quantum number into this article. These articles were all stubs (azimuthal is mostly redundant information). I do not believe that squeezing in this info bogs down this article, and it's a little more convenient for the reader to not have to go to the sub-articles just to get the basic idea what these numbers mean. Besides, some are calling for mergers among the articles on this topic.

In Summary of quantum numbers I removed the text saying "For instance, if n=2 l can be either 0 or 1" right after the article said "l can be any value in the range ${\displaystyle 0\leq l\leq n-1}$. That is superfluous text.

I expanded my original table so that it could include all existing labels for subshells, so it can lead to the explanation for these labels. I also put in the notation for a full fifth shell ahead of the relevant section because it better helps a reader understand its logic if he sees it right after the example.

--Kurzon 25 July, 2005

Please see my comments at the end of this page. (As a sidenote, you don't seem to have discovered the four-tilde (~~~~) signature.) --Smack (talk) 03:09, 26 July 2005 (UTC)

Electron shell, Orbitals, Atomic orbital, Electron configuration and possibly periodic table block should all be merged into a single article, preferably by someone who knows what they are talking about. The Anome

I put in a table which I believe betters helps students understand the logic behind shell configurations. I apologize for the frequent edits; I'll be more careful in the future. --Kurzon

No, they shouldn't all be merged. At the very least, each article should remain a stub. For instance, if you redirect from Electron shell to Atomic orbital, you give people the impression that they're the same thing, which is not true. --Smack (talk) 02:59, 25 July 2005 (UTC)
I agree that they shouldn't be merged. But it would be nice to have a clearer line between what information belongs in what topic. I think it would be good for Atomic orbital to have a quantum mechanical explanation along the lines of the Hydrogen-like atom and what the various quantum numbers mean. On the other hand, Electron configuration needs to explain things like Hunds rule, and how the overall magnetic moment, etc. arise because of the interactions between orbital, maybe even explaining the singlet-triplet splitting of He as an example.Mattopia 13:43, 23 October 2005 (UTC)
definitly no merge: it goes against the modular wiki approach, If you want to write large comprehensive articles better go to wiki books. The merge notice is almost 2 months old, does not have majority support so should be removed within 7 days V8rik 22:58, 25 October 2005 (UTC)

OK, I've had a go at it; I'll set about redirecting all those other pages. I'm a bit worried that the new version is a bit too Quantum Mechanical right from the off; I did try at first to write it describing the way it all works and then explaining the QM behind it at the end but it felt like a clumsy structure. If anyone feels like finding/making some pictures I think it'd be nice to have: some 3-D plots of the shapes of some of the more interesting orbitals, the energy level diagram (to replace the fixed-width thing at the moment) and possibly a diagram to illustrate the l/m_l magnitude-of-vector/projection-of-vector-on-z-axis analogy. Depending on how much free time I end up with this weekend I may even try making some myself. --Bth

doesn't the p shell have 8 slots, not 6 as it says in the table? (I might be wrong. Long time since last did chem) -- Tarquin
The article is correct, p only has 6. Which are; px, py and pz. There are no orbitals with 8 electrons, but the second energy level does have 8, so that may be where the confusion is coming from. Hm, come to think of it we need a good explanation on how these two systems relate to one another. --mav
Dammit, I had that in the draft at one stage but it got lost in the transition. How's the new bit? --Bth 08:00 Sep 27, 2002 (UTC)

Ok, a pet peeve. We can talk Legendre polynomials all day long, and its as if I really do care (not), but no one has seen to explain how the s orbitals were named s, the p were named p, d named d, etc. It *is* a nice story, digs up something about the history of spectroscopy, and puts a descriptive face on something the physics types can easily bury in the math of it all. If you don't remember, they're named after the characteristics of spectral lines. (s)trong, (p)rincipal, (d)iffuse, (f)undamental, etc. This characterization of the lines came before quantum theory was invented. I don't have the entire story off the top of my head, else I'd just write it. David M

That does sound interesting and I do vaguely remember one of my college chem profs mention that during one class. I will keep an eye out for the specifics. --mav
It probably belongs in another article, a history of spectroscopy, but with proper linkage back and forth, could add some descriptive color to this topic.dwmyers

## Recent edits by Kurzon and anon

I took the liberty of reverting the addition of new information about the quantum numbers, but such a change demands an explanation. This new information is superfluous and out of place; there's a better discussion of this topic at Atomic orbital. Furthermore, much of it was factually incorrect. --Smack (talk) 03:14, 25 July 2005 (UTC)

## Why electron configurations occur

I have removed the paragraph "Why electron configurations occur" because it is filled up with false assumptions.

The notion of electron configuration is predicated on three facts:

1. In a confined space, such as an atom or molecule, the energy and other properties of an electron are quantized, or restricted to certain possible states. The possible states are determined by electron orbitals. Each state generally has a different energy than any other state.
2. Electrons are fermions and are thus subject to the Pauli exclusion principle, which states that no two fermions can occupy the same quantum state at once. Once a state is occupied by an electron, the next electron must occupy a different state. In atoms, quantum states are determined by the values of four quantum numbers.
3. An electron is not stable if it is not in the state with the lowest possible energy. If a state with lower energy is available, the electron will, given time, switch to that state (and emit its excess energy as a photon).

As a result, any system has only one stable electron configuration. If left in equilibrium, it will always have this configuration (called the ground state), though the electrons may be temporarily "excited" to other configurations.

The electron configuration of a system is determined by its orbitals and by the number of electrons present. If one wishes to deduce the configuration, one must know the orbitals. This is relatively simple for hydrogen, much more difficult for other atoms, and even more difficult for molecules.

1. The title is a non sense : a configuration is a concept which does not occur but is usefull.
2. The correct title should be : "why do electronic atomic/molecular bound states exist?" i.e. "why does the electronic molecular Hamiltonian possess bound states?" whose answer is "because the nuclei attract the electrons" or "because the Coulomb potential is attractive enough" and not because an atom/molecule is a confined space.
3. An atom or a molecule is not a confined space
4. The energy of the electrons are not quantized but the energy of the atom/molecules are quantized.
5. A molecule in an excited state can switch back to the ground state without emitting any photon.
6. A excited molecule/atom can switch back to the ground state by emitting an Auger electron
--131.220.68.177 10:08, 8 August 2005 (UTC)
Half agree, but disagree with most of the changes. I'm not sure about the Chemistry side, but I think that electron configurations are a very useful concept. In my field (solid state physics), we estimate the magnetic dipole moment of atoms in crystals from the expected electron configuration. Maybe it should be pointed out that this is just an estimate, i.e. that the electron configurations cannot tell the true story of an ion in an ionic solid, or for that matter, any other solid. Still, approximations/generalizations are the nature of science, and so I think the title is spot on, and it seems to me to be the description that has been used for this concept for a long time. Mattopia 17:18, 5 November 2005 (UTC)

## Order in Exceptions

I was wondering why the exceptions section listed the 4s orbitals before some of the 3 orbitals. Is this standard in any field ? Mattopia 17:20, 5 November 2005 (UTC)

The 4s subshell is lower in energy than the 3d subshell so it appears before the 3d when writing out the electronic configuration, this is widely used, and perfectly acceptable. Perhaps this article would benefit from having a diagram showing the energies of the orbitals to give a clearer picture of the filling order. Lewis 14:29, 17 January 2006 (UTC)

## F-block?

Why do the first few f-block elements have d-orbital electrons rather than the expected f orbitals? MrHumperdink 04:51, 7 November 2005 (UTC)

## Confusing tag

I disagree with this. I think that the problem is on the Atomic orbital page, not this page. The electron configuration is basically a list of the atomic orbitals that are occupied. It would seem impossible to define the electron configuration without reference to atomic orbitals. I think the link at the top of the Atomic orbital page should be removed, and perhaps more fundamental or easily accessible material should be added there. Mattopia 12:40, 16 January 2006 (UTC)
I can see your point, but I don't have the expertise to make it happen. Be bold! --James S. 03:54, 17 January 2006 (UTC)
OK, I changed a lot of the start of the atomic orbital page (but not really wikified very well). See what you think. Mattopia 10:14, 17 January 2006 (UTC)
I think that the two articles should really be merged into one comprehensive article. Just looking at the top page of each of them, it's pretty difficult to tell what material each article covers or what is distinct information. In my opinion, electron configuration is a subset of atomic orbital theory and should be merged into that article. --—Preceding unsigned comment added by 12.33.19.11 (talk)
I disagree with a merge, it may be that the two articles have overlap, but there is a distinct difference between atomic orbitals (which describes atoms, and indeed, have an electronic configuration) and electron configuration (which also describes molecules and 'bodies' (clusters, metals). Molecules and 'bodies' need another explanation than atoms. It may be that there is info that should not be in one or the other article, that can be moved, but I strongly oppose a merge. --Dirk Beetstra T C 16:07, 11 August 2006 (UTC)

## Further exceptions

I think it should be noted that in transistion metals there is a further exception to electron filling rules. Ionization in these elemtents usually occurs in the s shell; not the d shell, and the resulting ion rarely has any s orbital valence electrons.

## Merge Things

There have been two merge headers added to this article. The poster hasn't given any reasons for the merges on the talk page, so I propose that the merge things are removed unless there is any argument for them (my own personal opinion is that the merges are unwarranted). I will remove the merge notices in a couple of weeks if there is no disagreement. Mattopia 18:33, 17 February 2006 (UTC)

• These merges would make the combined article too big. Best not to merge. Anthony Appleyard 11:22, 19 February 2006 (UTC)
• I see no reason to merge V8rik 18:21, 19 February 2006 (UTC)
• The merger is unwarranted, and there is no reason for it. HoCkEy_PUCK 00:03, 22 February 2006 (UTC)
• nobody in favor - vote closed - merge notice removed V8rik 00:16, 22 February 2006 (UTC)
I looked back at the pages that were suggested to be merged with this one, and there seems to be good reason for it. I've been looking at a bunch of pages about this sort of thing including quantum state, excited state, energy level, atomic orbitals, electron shell and this page electron configuration.
It seems like the same sort of information is covered in many related articles. It makes it difficult to find the information you need when the information is spread out through so many articles.
Its been said that merges would make the articles too big - I have a couple responses to that:
• Long articles aren't bad if they're well organized (which I doubt will happen anytime soon),
• Choosing subsections to be new pages would split the page into clearly defined subjects (as opposed to the nebulously different subjects of electron configuration and atomic orbitals.. and energy levels .. etc),
• Topics can be combined, shortened, and cut to make the page more handlable
• This page isn't very long as of right now, and good clean merges won't make it cumbersomely long.
I'd like to open the merge issue to discussion again, as I find these many interrelated articles hard to navigate as "separate" topics - when they really should be introduced in the same place. Fresheneesz 03:02, 22 May 2006 (UTC)

## Questions on Orbital Shapes

I know very little on the subject matter, but I noticed that the S1 and S2 orbits were spheres surrounding the nucleus and each S orbital is only able to contain 2 electrons max, but still the P orbital intersects the S orbital, due to their flower like shape. My question is how can it be that math predicts a P orbital can contain an electron that is both in the S orbit and the P orbit, when the S orbit is filled before the P orbit. --Shinjiro 02:00, 4 March 2006 (UTC)

While it may look like they intersect, a single electron can only occur in one given orbital at any given moment. The S orbit does fill first. Even though the P orbital penetrates closer to the nucleus, it also extends farther from the nucleus resulting in a higher energy orbit. This is difficult to visualize at first. The d-orbitals become even more confusing. Katze015 17:34, 25 July 2006 (UTC)

I would really like to see a more detailed (and mathematical) explanation of why orbitals are shaped like they are. What are the equations used to create the diagrams of the subshells (first and third picture)? If that's considered to be too technical for this article, there should at least be a link to an article containing this math. --Quuxman (talk) 05:37, 23 October 2011 (UTC)

Orbital shapes are explained to some extent in the articles on atomic orbital and molecular orbital. This article is concerned with the question of how many electrons occupy each orbital. Dirac66 (talk) 12:36, 23 October 2011 (UTC)

## Should "more" be "less"?

A pair of electrons with identical spins has slightly more energy than a pair of electrons with opposite spins. Since two electrons in the same orbital must have opposite spins, this causes electrons to prefer to occupy different orbitals.

I'll look this up later, but I'm in a hurry now. Or someone who knows more about spectroscopy could fix it. Thisrod 23:27, 7 March 2006 (UTC)

According to the Hund's Rule and Aufbau principle pages cited, high-spin is more stable, so "less energy" would be correct when the spins are aligned. However, the whole sense of cause/effect (spin-aligned is the primary source of stability, and therefore they must be in different orbitals) seems wrong. It appears that it is more stable to have electrons in different orbitals, and given that, it's even more stable to have them spin-aligned. DMacks 23:52, 7 March 2006 (UTC)
On re-re-reading Hund's Rule, it becomes less clear what the driving force is (different m or different s). DMacks 23:58, 7 March 2006 (UTC)

## image

That table is incomplete, should be updated

## Electronic structure

Electronic structure redirects here, but that is quite misleading. Electronic structure applies to all methods of quantum chemistry, while electron configuration applies only to methods using molecular orbitals. Does anyone have suggestions how to deal with this? --Bduke 03:28, 11 April 2006 (UTC)

Well, you could start a stub. What does "electronic structure" refer to if not orbitals in an atom or molecule? Fresheneesz 03:11, 22 May 2006 (UTC)
Like I said back on 11 April, all methods of quantum chemistry. Orbitals are only part of certain approximate methods of quantum chemistry, not all. We need to distinguish a reasonably elementary level of discourse here, where electron configuration is the way to go, and more advanced approaches to electronic structure where electron configurations and orbitals may have no role. I'll try to get back to this and think about it more carefully. --Bduke 13:01, 22 May 2006 (UTC)
I meant to ask for examples. Fresheneesz 02:15, 23 May 2006 (UTC)

## Electron configurations of ions

I'd like to see a section for configurations of ions, because I had assumed that the configuration for Fe2+ should be identical to that of Cr. Then I was told (by an unreliable source) that you always remove the s electrons first no matter what, so that Fe2+ should amount to [Ar]3d6 rather than Cr's [Ar]3d54s1. Can anyone clarify this for me and make such a statement on the main page, for whether I'm right or wrong? And can anyone tell why W (Z=74) and Sg (Z=106) don't match Cr's configuration? D. F. Schmidt 14:08, 9 June 2006 (UTC)

## Colored Compounds

I think that it should be noted in this article that colored compounds are caused by the electrons that fill the d-orbital. In polar molecules and charged ions, the d-orbital splits into lower energy and higher energy. The color is caused by electrons moving with in these two sections of the d-orbital. However, I am not an expert on this subject and I will leave it to someone who knows more about the subject.

Colored compounds are not restricted to compounds that have electrons in d orbitals. Colors of flowers are one example. --Bduke 01:00, 5 November 2006 (UTC)

## Electron orbital picture

Can someone explain why the image comes out black when printed or copied to Photoshop? And why is it in such an obscure format as .svg? Should or could this be converted into, say, .png for better viewing/printing? - Quirk 14:45, 15 November 2006 (UTC)

• I don't find svg obscure. It is an open standard based on XML, see svg. It is a vector format, so it is better than .png for vector graphics. A .svgz file may even be smaller than a comparable-quality .png. 147.32.82.16 (talk) 08:44, 16 December 2010 (UTC)
• It was much more obscure (or at least not as widely supported) in 2006, when the poster asked about it:) DMacks (talk) 14:44, 16 December 2010 (UTC)

## Insufficient Context Notice

Hi! I'm new here, but willing to take a stab at rewriting the introductory paragraphs. Here's a first draft.

In atomic physics and quantum chemistry, the electron configuration is the arrangement of electrons in an atom, molecule, or other physical structure (eg, a crystal).

Like other elementary particles, the electron is subject to the laws of quantum mechanics, and exhibits both particle-like and wave-like properties. Formally, the quantum state of a particular electron is defined by its wavefunction, a complex-valued function of space and time. According to the Copenhagen interpretation of quantum mechanics, a particular electron is both "nowhere at all" and "everywhere all at once" until an act of measurement causes it to be detected. The probability that the act of measurement will detect the electron at a particular point in space is proportional to the square of the absolute value of the wavefunction at that point.

Electrons are able to jump from one energy level to another by emission or absorption of a quantum of energy, in the form of a photon. Because of the Pauli exclusion principle, no more than two electrons may exist in a given atomic orbital; therefore an electron may only leap to another orbital if there is a vacancy there.

Is this better? DavidCBryant 20:12, 21 November 2006 (UTC)

## Isn't this an encyclopaedia?

Sorry to stampede in here, but as this is an encyclopaedia and not a textbook, shouldn't a more substantial effort be made to render this information comprehensible to people who aren't post-grad chemists or physicists? At least some of the subject matter treated on this page could in principle be rendered comprehensible to intelligent laypersons, and in fact frequently is in textbooks with far less ecumenical pretensions than wikipedia.Jamrifis 17:14, 28 June 2007 (UTC)

i guess nobodys going to fix this:) i at least suggest an image of rings around the nucleus with the orbitals labeled so i can understand the more complex diagrams.121.223.15.48 (talk) 11:14, 28 January 2012 (UTC)

i will add an example image of the above comment, will need a redraw. see image comments.

Charlieb000 (talk) 20:35, 28 January 2012 (UTC)

## Does this belong in the lead?

I was going to remove this from the lead as it seems not to be particulary relevant, as least as being the lead. (wikilinks removed when copying)

Like other elementary particles, the electron is subject to the laws of quantum mechanics, and exhibits both particle-like and wave-like properties. Formally, the quantum state of a particular electron is defined by its wavefunction, a complex-valued function of space and time. According to the Copenhagen interpretation of quantum mechanics, the position of a particular electron is not well defined until an act of measurement causes it to be detected. The probability that the act of measurement will detect the electron at a particular point in space is proportional to the square of the absolute value of the wavefunction at that point.

It seems to me the lead should describe rather that the configuration is a description which summarizes the quantum states, as opposed to commenting on the nature of quantum states in general. Comments? Baccyak4H (Yak!) 13:53, 24 August 2007 (UTC)

I agree. I think this needs to be rewritten and moved further down and a much more brief mention made in the lead. The aim of the rewrite should be to stress that the idea of electron configuration is an approximation to the full quantum description of an atom. --Bduke 21:58, 24 August 2007 (UTC)

## proposed deletion: "with the exception of Lawrencium (element 103), which would require a 7p orbital"

Orbitals table
This table shows all orbital configurations up to 7s, therefore it covers the simple
electronic configuration for all elements from the periodic table up to Ununbium (element 112)
with the exception of Lawrencium (element 103), which would require a 7p orbital.


in all the periodic tables i have checked there is no reference to a 7p orbital in Lawrencium (and it wouldn't make any sense a p orbital in the middle of the periodic table! i'm wondering if this is subtle vandalism or just a check?) --Eumeme (talk) 01:54, 29 January 2008 (UTC)

i've checked the network - the probable configuration has indeed an electron on the 7p orbital - exception is the rule in chemistry! the current Lawrencium configuration is not correct then... --Eumeme (talk) 02:20, 29 January 2008 (UTC)

## Simple method for deriving electronic configurations.

There is simple method for deriving electronic configuration: Electronic Configuration Chart.

It is based on modified Left Step Periodic Table (1928) and is easy to use. It works very well and praised by few chemistry teachers.

I'd like to add the above link to this article, if it is O.K. with everybody here. What would be a good place for it?

Drova (talk) 17:46, 5 June 2008 (UTC)

## Chages introduced by Weekwhom on July 1, 2008

The list of orbital image links at the bottom of the page is very long. Could it be presented in more organized way? Also, there is a table of orbital images already there. Do we need more of the same? 68.48.234.55 (talk) 14:03, 1 July 2008 (UTC)

Concurred...I removed all those links. If the goal is to provide a reference to support something that was previously unsupported or controversial (WP:AGF for the edits), it's not clear what it supported. The images themselves are mathematically generated, with cites in the images themselves. Citing them to some other site is not even correct, since those sites aren't the source for those images or the information contained in them. It crosses spam (or at least external-links) guidelines to have all those links, since there doesn't appear to be any content there that isn't or couldn't be included in WP itself. At most, I would consider one link to the site in the External links section. DMacks (talk) 15:22, 1 July 2008 (UTC)

## Exceptions to the Aufbau principle

The d-block exceptions to the Aufbau principle are admirably dealt with in this article. However, I noticed that apart from a passing reference to Lawrencium, none of the Lanthanoid or Actinoid elements are discussed, despite the fact that the electron configurations periodic table quite clearly lists numerous exceptions which cannot be explained away as easily, since they do not result in a half-full shell. Does anyone know of a simple reason why this occurs? Should these exceptions be mentioned in the article even if the reason is unknown? Thanks, Rundquist (talk) 01:42, 18 July 2008 (UTC)

## Notation for types of orbitals needs explanation

Even after reading this article, I do not understand why the orbitals must be distinguished by letter (s, p, d, f, g) during notation and what the effects of this (the meaning of the representation provided by the letters, seeing as how different random squiggles being used probably does not affect quantum mechanics) are. Could this be explained in the article (for I believe that there probably are many other people out there who have my same problem)? If it is done so (already, or in response to this post), please notify me here. Thank you. 98.27.163.42 (talk) 20:39, 20 August 2008 (UTC)

Well, you have to have some way to indicate which orbital you're talking about. The letters don't have actual meaning though, they're just symbols. Everywhere I see them described on this page, they are just used as arbitrary symbols or else as letters that correspond to different angular-momentum values. It's explained in detail the atomic orbital page (which is linked as an important backround article for the one here). DMacks (talk) 21:43, 20 August 2008 (UTC)
Thanks. After reading the other article, may I come back here for further help? Or should I post on that talk page? Or in your talk page? 98.27.163.42 (talk) 00:30, 24 August 2008 (UTC)
The section Notation explains this, since at least 2005. One could place Notation earlier or refer to it where it is first used, but if it would help those without the patience to work through the article, I do not know - the latter would bloat the text a little. PJTraill (talk) 14:13, 3 October 2008 (UTC)
As the article points out, the choice of letters comes from an old system of labelling spectral lines: sharp, principal, diffuse, fine. The different letters indicate different shapes of orbital: s-orbitals are spherically symmetrical, p-orbitals are sort of dumb-bell shaped with two distinct lobes, d-orbitals have four lobes and f-orbitals have eight lobes. Mathematically, they come from different spherical harmonics. Physchim62 (talk) 23:20, 3 October 2008 (UTC)

## Redundancy with other articles

There seems to be a great deal of redundancy between this article and various others: Atomic orbital, Electron cloud (proposed for merge), Molecular orbital theory, Molecular orbital, .. and there are probably more, to be found by some sort of search. Some sort of merging and/or reorganisation seems to be called for. PJTraill (talk) 13:57, 3 October 2008 (UTC)

N.B. Sorry, I see that this is an old discussion, just that the sections discussing it have misleading titles or mixed content — but the point remains valid: it is still a muddle. Since it seems a job for the project, I have added the section Wikipedia talk:WikiProject Physics#Organisation of orbital articles PJTraill (talk) 14:28, 3 October 2008 (UTC)
While I agree to some extend that there is some muddle, I disagree in both your analysis and your conclusion. I think these are linked. For the conclusion, this should be looked at primarily by the Chemistry Project. These topics are prime chemistry topics. Chemists, I think, would argue for keeping these topics separate. There might be a case for merging Molecular orbital into Molecular orbital theory. Electron cloud should not just be about atoms, so a merge into Atomic orbital is inappropriate. Also that merge proposal is inadequate as it does not tag the target article, Atomic orbital, and hence does not inform the editors who work on that article unless they also work on Electron cloud. I will fix the merge proposal. --Bduke (Discussion) 23:08, 3 October 2008 (UTC)

You're almost certainly right about the redundancy between this article and Aufbau principle; I piled in yesterday to try to clear up some of the other mess that was here, and I may well have gone OTT. I'll try to finish the sections on history and applications today, an then take a look at the balance of the whole thing.
As for the status of the Madelung rule, I find it hard to grant it experimental status. Electron configurations were "derived" experimentally, from the indexing of atomic spectra. The Madelung rule is just a heuristic which covers 80% of ground-state electron configurations. The only people who lose sleep over the fact that there are exceptions to the Madelung rule are freshman chem students who are trying to learn electron configurations.
Scerri (and others before him) makes a big point that the Madelung rule has never been derived from first principles; if anything, I would go further and say that the only thing we have any right to expect from first principles is a rule of the form (n, l), not (n+l, n). The Madelung rule only "works" because the electron configurations (and the periodic table) were already known, and so it could be fixed to give the (80%) right answer! To me, that's description, not explanation. Physchim62 (talk) 07:45, 5 October 2008 (UTC)

I actually agree with you that Madelung rule is only about 80% right and is not an explanation, but more of a description. What I have a problem with is the word "conceived". The Madelung rule was "derived" or "discovered" by looking at the electron configurations. I believe that the root of the problem is misunderstanding of quantum numbers "n" and "l" and their relationship between themselves. For example, it is said that Madelung rule is (n+l, n). That is so if l=0,1,...(n-1). Same Madelung rule could be simply (n+l) rule if l=(n-1),(n-2), ...1,0. I view the Madelung rule as a part of relationship between "n" and "l" that is not sufficiently understood. The problem is in the popular definition of "l" through "n", which, I believe, is too simplistic. That is why, if we simply solve Schroedinger equation straight, that is using current definition of "l", we would have elements in subshell 5g in the current periodic system, corresponding to l=5-1=4. We could simply explain it away using energy, etc. But "l" reflects the magnitude of the angular momentum. And why is energy and the angular momentum together acting like that? All previous explanations of "n+1" simply expalain it away, and not really explain it and that is the big deal. Well, this discussion goes beyond the scope of Wiki article. My issue with the word "conceived". Could you come up with a better word?Drova (talk) 13:18, 5 October 2008 (UTC)

I'll certainly try to find a better alternative to "conceived" if that's what's bothering you in the article! You can get explanations of the variance of orbital energy with l by taking l not as an angular momentum measure but simply as the number of angular nodes in the wavefunction: unfortunately, they also introduce paradoxes with observed chemistry, so I haven't mentioned them here. Physchim62 (talk) 15:59, 5 October 2008 (UTC)

## Need Help

User Arthur Rubin, who appears to have no expertise in this subject, based on his previous contributions, have tried to remove the link to Simplified procedure for determination of electron configurations twice. The link has been there since last June and was viewed and supported by many. What can be done to stop him from doing this? Drova (talk) 21:39, 29 October 2008 (UTC)

Name one person who "supported" it. It's a personal web site, from a person without a claim of expertise. How is this not a good example of WP:ELNO#11?
The web site itself has Comments section, if you need outside source check this out: [1] there are many more like this, but the experts know that the metod is simplified and works.Drova (talk) 21:58, 29 October 2008 (UTC)
Nonsense. It's not simplified, and still violates WP:ELNO#11. Please do not remove the {{dubious}} tag without consensus. Now, if you were to use the original 1929 paper referred to in one of the talk pages as a reference, I would have no objection, but the web site is not usable. — Arthur Rubin (talk) 22:09, 29 October 2008 (UTC)

I will not remove word "dubious". I'd like to hear other opinions.Drova (talk) 22:15, 29 October 2008 (UTC)

Appears to be self-published and self-admitedly at odds with current scientific theories (electrons per level) therefore WP:FRINGE at best. Or would be if it were actually a WP:RS. But all we have is a novel demonstration or mnemonic device, not a proof of anything (extending a model beyond its known realm without testing its predictions is sci-fi not accepted science). DMacks (talk) 02:19, 30 October 2008 (UTC)
The novelty is in arrangement of the periodic table in accordance with the Madelung rule. The the web page in question, that the article is linked to, does not make any predictions, etc. Both, periodic table and the Madelung rule are existing and well known concepts. All it does, demonstrates simple method of deriving electron configurations. Is this really a FRINGE?Drova (talk) 12:31, 30 October 2008 (UTC)

(outside input) After reading this website, I am not (yet) prepared to call it "fringe", but as a source for this article it should be omitted. The source is self published and clearly more of a recreational/conjectorial nature, something more attuned to a Martin Gardener book than for a source for a Wikipedia article (unless the article about the novelty itself...). The article is better without it, as plenty of other reliable and high quality refs exist. Baccyak4H (Yak!) 16:41, 30 October 2008 (UTC)

I think you are confusing the source with the external link. External links are for enhancing only and do not serve as basis for the article. They are intended to go beyond the issues discussed in the article. In accordance with Webster's Dictionary "Encyclopedia is a book, covering all branches of knowledge or, less commonly, all aspects of one subject". If Wikipedia is intended to be a good encyclopedia, it should cover as many aspects of any particular subject as possible. The link has been there since early June. No one had any concerns until few days ago. Thanks anyway, for not calling it a fringeDrova (talk)
You're welcome. I was talking about sourcing, yes, but upon exchanging the words in my above comment, I have to maintain the view that it's not a good external link either, noting the same issues with the link, although quoting WP:EL, in particular #4 here and the noncommercial mention here. In addition, while the following reference wass written to pertain to article topic, that page is basically somebody's pet project, so again, this is not appropriate in spirit for inclusion. Your claim about many aspects is true up to the point of facilitating a quality encyclopedia; the spirit of allowing such a link would enable a lot of random people to use the project as a free web host for their pet ideas, and that is certainly contrary to building a quality encyclopedia.
Do keep in mind I haven't even looked at the article since June (or earlier), until a day or so ago, and that may be the situation for others. So the arguments themselves, not the temporal gap between them, should be considered. Baccyak4H (Yak!) 19:46, 30 October 2008 (UTC)
I understand your point in regard to [[WP:EL#AVOID| #4. However, I believe it also provides for some flexibility. This posting makes good arguments in favor of the electron configuration determination procedure described in the link discussed here. It demonstrates its usefulness for chemistry teachers and those who they are trying to teach. I remember, when I was student, electron configurations were the hardest to learn using the conventional PT and the Madelung mnemonic. While using PT presented in the link you do not need the mnemonics. Madelung rule is embedded in it. Of course, if you have doctorate in chemistry, you know the electron configurations by hart. But for thouse who are learning them, it is of great help. I can not say it any better. I'd wish I could link to other site that describes such procedure, to avoid your concerns, but I am not aware of such.Drova (talk) 21:33, 30 October 2008 (UTC)
I agree that this link goes against the Wikipedia external linking policy. In fact, for this topic I don't think we need any external links at all. --Itub (talk) 14:01, 31 October 2008 (UTC)
Thought you might want to know that Dr.Philip J. Stewart of Oxford in his article entitled "Charles Janet: unrecognized genius of the periodic system." printed in Foundations of Chemistry, January, 2009 issue (ISSN 1386-4238 (Print) ISSN 1572-8463 (Online)) wrote following: "An interesting improvement to the Janet table has been made by Tsimmerman (2007), who shifts the p, d and f blocks so that each electron shell is represented by a single row (or column if turned through 90 degrees), displaying a symmetry that was not evident in the original." He also included ADOMAH PT web site in the references.Drova (talk) 18:49, 29 January 2009 (UTC)
Still violates WP:ELNO. That article, potentially, is a reference, but not ADOMAH PT. Furthermore, calling it "simplified" is your (and the web page owner's) POV, not provided in a reliable source, as of yet. — Arthur Rubin (talk) 19:24, 10 February 2009 (UTC)

So, derivation of electron configurations has no value for the above wikiers! Wow! Perhaps they know them by hart, or those who do not could simply look it up. Right?

Does the article address question how electron configurations are derived? What is procedure for deriving electron configurations? Perhaps you can add few simple sentences to the article in that regard just to make it useful? As simple as those used here? ;) Drova (talk) 00:24, 11 February 2009 (UTC)

That's not how they are derived. It's an alternate explanation of the orbitals, based (essentially) on the fact the electron energies are approximately related to the quantum number n+l, then in decreasing order of l. It's possibly a useful mnenomic, although we'd need a reference for that. (And not the web page, unless some reliable source thinks it notable and reliable.) — Arthur Rubin (talk) 01:30, 11 February 2009 (UTC)

So, how are they derived? Is there simple step by step procedure? Is periodic table needed at all, or just a mnemonic? May be you could give us an example how to derive electron configuration of Er? Just few simple sentences, please.

On the other note, the derivation procedure is direct consequence of shifting p,d,f blocks to align shell numbers that is deemed notable and reliable by "Foundations of Chemistry" journal that is printed on paper, as well as on the web. The ability to derive electron configurations is direct outcome of that shift. It is obvious and can be easily verified by anyone who is familiar with the subject. That is enough source for the link. Similarly, shapes of electron clouds presented in the single remaining link is outcome of solutions of Schrodinger equation. Did you verify their accuracy? What is the source for that link? Why do you consider that link reliable and not the other one? Drova (talk) 01:37, 11 February 2009 (UTC)

I think that enough time was given to the above detractors to present us with a procedure of deriving electron configuration and to answer the above questions. Apparently they couldn't. Since it is beneficial to have at least one such procedure in the article, I decided to restore the link.-Drova (talk) 13:41, 3 March 2009 (UTC)
Your arguments are to the concept, which I don't think is notable, but could be convinced if you gave a reference. The web site is a personal web site of a person who is probably not considered reliable per se. In my opinion, one, at the least, would need to be immediately recognized by anyone in the field for that to be the case. — Arthur Rubin (talk) 15:32, 3 March 2009 (UTC)
What about remaining link there? Does it meet the same criteria? Is it presented by a person who is immediately recognized by anyone in the field?-Drova (talk) 15:46, 3 March 2009 (UTC)
I can't easily find whose web site it is. If you can demonstrate it's not sponsored by the university, and it is not a reprint from a published book, then it probably should go, also. — Arthur Rubin (talk) 15:52, 3 March 2009 (UTC)
By university? I havn't seen such requirement for the links before? ADOMAH PT was published in well known Chemogenesis Webbook. Is that good enough.Drova (talk) 16:14, 3 March 2009 (UTC)
The hydrogenlab.de site "Imprint" page states explicitly that is by a university physics professor and associates. That would lead me to say it's a RS: academic researchers talking in their field/etc., and so we would presume a respectable & trustable source of information. Assuming it is in keeping with the views presented in the WP page here, it therefore meets EL guidelines as being informative, on-topic, good information/extension of article itself but not includeable in the article itself. My only concern is that t here is a lot of Flash there, which is not very accessible (another EL criterion). DMacks (talk) 16:23, 3 March 2009 (UTC)
I don't know if the Chemogensis Webbook is reliable, but it probably would meet the weaker reliability standards for external links. However, the electron configuration page of your site doesn't seem to be there, only the periodic table page. Being linked from there is certainly not adequate. — Arthur Rubin (talk) 16:25, 3 March 2009 (UTC)

dear Arthur, Read 2009 January Issue of "Foundations of Chemistry", Article "Charles janet, unrecognized genius of periodic system" by Oxford professor Dr. Philip Stewart. It says clearly, that colums of ADOMAH Periodic Table depict electron shells. That is why it has natural symmetry and considered to be improvement to Janet's Left Step Periodic Table. Sorry, the link you have removed was relevant and important for the article, therefore it should be restored. Please, do it yourself or let me do it.Drova (talk) 15:01, 11 February 2010 (UTC)

As I said before, that article is potentially a reference, although I'd have to see a copy to be sure. Your periodic table is not, even potentially, an external link here. It may be a relevant link to alternative periodic tables. — Arthur Rubin (talk) 16:03, 11 February 2010 (UTC)
please, review the article. Also, I would like to direct you to the list of References at the end of the article that directly lists www.perfectperiodictable.com web site (the link removed by you).Drova (talk) 17:05, 11 February 2010 (UTC)
I don't have a journal subscription, so I cannot review the article, unless the author has posted it somewhere. However, it should be noted that "Foundations of Chemistry" is categorized as "Humanities, Social Sciences and Law", rather than as an actual Science journal, so it also probably wouldn't be appropriate for this article. — Arthur Rubin (talk) 18:36, 11 February 2010 (UTC)
"Foundations of Chemistry" covers History of Chemistry, Philosophy of Chemistry and some chemical education issues. It has a middling reputation I feel, and is certainly not read by most chemists, but is one of two must reads for philosophers of chemistry. Email me and tell me what you want to check in that article and I'll have a look. I think I still have access to it. --Bduke (Discussion) 22:00, 11 February 2010 (UTC)
The reference above for this article in "Foundations of Chemistry" is incorrect. It was published online in January 2010 (not 2009) and therefore it will presumably be in Issue 1 of Volume 12 in April 2010. The journal has published three issues per year in April, July and October since 2007. --Bduke (Discussion) 22:39, 11 February 2010 (UTC)
I have discussed this paper's reference on Talk:Alternative periodic tables, as it is a reference on that article. In brief it was published in advance on the web site of the journal in January, 2009, but it has not yet appeared in the paper publication and appears to be set for Volume 12 in 2010, a long gap between acceptance and full publication. I was mistaken in the comment immediately above. I had not understood the long gap. --Bduke (Discussion) 05:21, 12 February 2010 (UTC)
It was published, finnaly. See Foundations of Chemistry Vol.12, No.1 April, 2010; Drova (talk) 21:46, 14 October 2010 (UTC)

## Shells and Subshells: Undefined label

The section starts using the label "l" without mentioning that it stands for azimuthal quantum number. Though the concept is dealt with in the previous section, the label is not, and probably confusing to those not familiar with its conventional use in the context. A simple phrase or two would fix it.

## What electron configuration are.

There is a lot of debate on how to determine electron configurations. It might be useful to remember that electron configurations are only models based on calculations extrapolated from one electron systems. In the end the models have questionable relevance to reality. After all an isolated carbon atom in the ground state has the configuration of 1s2 2s2 2p2, but when was the last time anyone saw a isolated carbon atom in the ground state. My favorite is the care taken to describe transition metals like chromium and copper. I would like to see a single bit of experimental evidence where there is an electron in on of these elements 4s orbital and not siting in a d based orbital. The article should state that electron configurations are models that: A)helps us to understand the relative energies of atomic orbitals before they are incorporated into more complex system described best with MO theory or valence bond theory. B)the model is often used teach general chemistry students their quantum numbers. C)Don't relate to reality. I've stuck my foot in my mouth enough when trying to edit something best left to theoreticians. Likely I've done it again with this commentary. Regardless it would be nice if someone incorporated these concerns.--OMCV (talk) 04:41, 11 February 2009 (UTC)

I would agree with you on the only a model bit, but the one-electron hydrogenic atom allowed states do remain qualitatively useful in most cases (after extending for electron-electron effects, bands, molecular orbitals, and hybridization). The discrete energy levels may be measured by e.g. x-ray fluorescence or Raman scattering. If there are no objections, I would like to change the Electron configuration in solids section to describe band theory as an extension of the configuration model rather than an out-and-out replacement for it. It still makes sense to talk about a 3d band in bulk copper (or a 3d4s band in some compounds), and the lower energy electrons remain well-localized in orbitals pretty much the same as in bare atoms. An instructive example is the behavior of the 5f electrons across the actinide series - for the lighter elements, they form a narrow band in the bulk, but starting with americium they prefer to localize as individual subshells. This leads naturally into a discussion of changes in valence due to chemical environment (bare Am is s2, but in bulk crystal it is spd3), though that may be veering off topic for this article. - Eldereft (cont.) 16:02, 11 February 2009 (UTC)

OMCV wrote above that electron configurations have questionable relevance to reality. However, the n+l rule (although, not perfect) was discovered through the means of spectroscopy and is empirical. It is true that few valence electrons might not be in the ground state at all time, but inner shells, that are part of atom's core are in order. The electron configurations reflect the lowest possible energy state of the electrons, not the current energy state. I would not underestimate the importance of the concept of electron configurations.Drova (talk) 13:10, 12 February 2009 (UTC)

This discussion goes around a key point but never quite gets there. For example, OMCV asks "when was the last time anyone saw a isolated carbon atom in the ground state?". Well in a sense it was the last time someone observed the electronic spectrum of a carbon atom. This can really only be interpreted by saying that the ground state of the C atom is one of the 3P states. This state is the one predicted from the 1s22s22p2 configuration, so this is why we say that is the electron configuration. Note that this is not a rigorous derivation from experiment because the single configuration may not be a good approximation to the many-electron wave function. --Bduke (Discussion) 22:34, 12 February 2009 (UTC)

Like I said, I put my foot in the mouth. Drova, I would like to note the electron configuration represent the lowest energy state in a non-bonding situation. A non-bonding situation is really a very high energy electronic state for most atoms found in nature. Bduke's comment help and I plan to look up literature on the 3P states next time I have journal access. I didn't imagine anyone actually obtaining ground state neutral carbon atoms. I figured that form of carbon would be rather reactive. I imagined carbon plasma but I guess even a portion of the plasma would be in the neutral ground state. So is it true that all the configurations are based on experimental data or is it a portion and the rest are derived from extrapolation? Even if the configurations are based off experimental data shouldn't it be well explained that the ground state configuration represents an artificial state achieved under very specialized laboratory conditions, with the exception of the noble gases. It would be nice to have a little more information on the experimental foundation of this convention, even if this information isn't usually included in general chemistry textbooks. Information that goes beyond the electronic spectra of hydrogen. I always thought teaching and testing student on specific electron configurations (that don't relate to a naturally occurring systems) to be a pointless endeavor; like teaching and testing students on their ability to write in cursive. Maybe I'm wrong. I still think weak link between electron configurations and experimental evidence exacerbates the disconnect in students minds between representative chemistry and reality. Thanks for the comments, I'm not trying to be a crank.--OMCV (talk) 01:54, 13 February 2009 (UTC)
I really have no idea what you mean by "A non-bonding situation is really a very high energy electronic state for most atoms found in nature". The problem with electron configurations is that they are based on free gas phase atoms. Yes, these are higher in energy that the atoms in molecules or solids, but they are readily obtained and observed spectroscopically. The energy to promote the free atom from its ground state to an excited state is relatively high so even at high temperatures there are always a fair proportion of atoms in the ground state. The link between experiment and electron configurations is inevitably weak. One can guess a configuration for the free atom, then predict what state of the free atom corresponds to the configuration and then check that against spectroscopic evidence, but it does not rigorously deduce the electron configuration from experiment. One can however do that process for all known atoms. I sometimes think our periodic tables would be better not displaying electron configurations as they can be misleading for many elements such as transition metals. BTW, try books on atomic spectra or quantum chemistry, not journals. Atkins' "Molecular Quantum Mechanics" has a good section on atomic spectra. --Bduke (Discussion) 02:24, 13 February 2009 (UTC)
Of course I am talking about atoms that are neutral, in non-bonding condition, just as they are presented in the Periodic Table, that remains useful despite the fact that many atoms are not typically found in nature in pure form. Treating elements as basic substances goes back to Mendeleev and even earlier. Neither Schrödinger equation, nor other mathematical fits, such as Hartree-Fock, describe nature accurately. Many times it is useful to consider things in idealized manner. I think that periodic table should be based on electron configurations because it helps to highlight and explain exceptions, such as transition metals, by showing how they depart from the idealized condition. On the other hand, presenting sequence of elements in order of s,f,d,p for the purpose of ending periods with inert gases hits the road block when it comes to super heavy elements, where relativistic effects beginning to play a big role. That is the story with Uuq, as was recently reported and I am sure with all other heavy weights. Am I putting my foot in the mouth? Drova (talk) 05:09, 13 February 2009 (UTC)

## Symbol for element 105

I noticed that the Electron Configuration Table uses the old symbol HA in lieu of the now commonly used Db, which is used in the Periodic Table. This should be an easy fix but I am new to this process so I leave it as a suggestion. Wyzzsr (talk) 01:54, 8 November 2009 (UTC)

Yes, it should be Db which is now the official name - see Transfermium Wars. Unfortunately fixing a graphic is much harder than fixing the text, since only the user who made the graphic (Qbmaster) can modify its source file. I see that you have left a message on Qbmaster's talk page so hopefully s/he will change it. If not the only other way is to delete the incorrect graphic and redraw it, which would be a LOT of work so I don't recommend it. Dirac66 (talk) 03:27, 8 November 2009 (UTC)

## Energy - Ground State - Excited state

I find it extremely dissatisfying that this section is largely ignored in the electron configuration article. There should be at least a decent explanation on the excited state of electrons and its effects; on the actual definition of ground state; and the results of electrons dropping from excited states to their ground state (e.g. photon emissions). Additionally, there are several rules governing excitation that should be mentioned here, as well as the differences in energy levels between electron orbitals. (Fireyair (talk) 03:37, 8 October 2009 (UTC))

Well, be WP:BOLD and write it. If you have only an outline idea, write an encyclopedic language summary, with a ref, and put THAT in. At least it will start the thing. SBHarris 17:27, 11 February 2010 (UTC)
I have now added two more paragraphs at first-year chemistry level, using sodium as an example and mentioning the sodium-vapor lamp. Dirac66 (talk) 23:44, 11 February 2010 (UTC)

## Confusing example

"For atoms, the notation consists of a string of atomic orbital labels (eg, 1s, 2p, 3d, 4f)..." That's confusing. What is a "string"? Is that used in the sense of "sequence of alphanumeric characters"? Is "1s, 2p, 3d, 4f" one example, or four? What is one string? Is it "1s" or "1s, 2p, 3d, 4f"? Is "orbital" used as an adjective or a noun? To what are the labels applied? I suspect, but don't know, that "1s" is a label, and that it is used to identify an "atomic orbital". What the digit stands for and what the letter stands for aren't explained. Unfree (talk) 18:23, 27 February 2010 (UTC)

I have replaced "string" by "sequence" and changed the example to correspond to the sequence used in another example in the same paragraph. As for the notation used to identify orbitals, this is described in the preceding section "Shells and subshells". Dirac66 (talk) 19:25, 27 February 2010 (UTC)
Thanks. The word was probably intended to be "string", but sequence is a bit more dignified. SBHarris 22:53, 14 October 2010 (UTC)

## I'm sorry that I included the table to list chromium and copper.

I'm sorry to duplicate it, and plus, they called it "other" exceptions. — Preceding unsigned comment added by Wd930Bot (talkcontribs) 03:42, 15 December 2010 (UTC)

## Nickel - ground state or lowest average energy?

The recent inclusion of Ni with configuration 4s 3d9 is surprising, since most chemistry textbooks (including Miessler and Tarr, cited at the top of the table) show Ni as 4s2 3d8. Scerri’s Periodic Table book is now cited as one source for 4s 3d9, but since there are conflicting sources I think some further brief explanation is necessary for this table.

The problem for the nickel atom is that the sets of states arising from these two configurations overlap, so that the definition of the atomic configuration is somewhat ambiguous and not all authors agree.

The electronic ground state of the nickel atom arises is a (Ar)4s2 3d8 state, as agreed by Miessler and Tarr and many other textbooks and also by Scerri (p.239: “the lowest energy term arises from the 4s2 3d8 configuration”). The NIST listing of experimental atomic energy levels at http://physics.nist.gov/PhysRefData/ASD/levels_form.html (enter Ni I) shows the lowest energy term as 3d8(3F) 4s2 3F.

However Scerri points out that the research literature on atomic calculations invariably quotes the configuration of nickel as 4s1 3d9, because the average energy of its energy levels is lower than that the average for 4s2 3d8. This fact can be seen from the NIST listing, since the second and third lowest terms are the 3d9(2D) 4s(1,3D), while the remaining d8 s2 terms are at considerably higher energies.

The question is then whether to show the configuration of the ground state as in textbooks, or the configuration of lowest average energy as in the research literature (as per Scerri)? Since there is a genuine disagreement among reliable sources, I think that Wikipedia policy (WP:NPOV) requires mention of both with a brief explanation of why they disagree. Also, most of this Wikipedia article deals with ground state configurations, so any discussion of other states should be noted.

I think the simplest solution is to write both configurations in the table: [Ar] 4s2 3d8 (ground state in parentheses) and [Ar] 4s1 3d9 (lowest average energy). Dirac66 (talk) 02:53, 6 March 2011 (UTC)

The description of "lowest average energy" and "ground state" are rather misleading. To label 4s2 3d8 "ground state" as opposed to a "lowest average energy" for 4s1 3d9 may imply that the latter is not a ground state configuration, which is not the case. Also, the term "lowest average energy" is not well defined in the context, and may lead to more confusion, if it appears abruptly. I suggest leaving the word "disputed" here and let the cited source do the explanation, and the layout of the table will be better. --130.126.92.40 (talk) 09:21, 6 March 2011 (UTC)

What exactly do you mean by a ground state configuration? As I understand it, there is only one ground state configuration of each atom, and that is the configuration of its ground state or lowest energy term. For the nickel atom the NIST Atomic Spectra Database lists the lowest energy term as 3d8(3F) 4s2 3F based on experimental spectra. Therefore the ground state configuration is 3d8 4s2 (or 4s2 3d8), and 4s1 3d9 is not a ground state configuration. Dirac66 (talk) 14:57, 6 March 2011 (UTC)
The problem is that the 3d8 4s2 "state" is higher in energy than 3d9 4s1. BUT, the lowests energy J state is a 3d8 4s2 J state. The end result is that the question of which is lower is actually wrong. The lowest state is "a" 3d8 4s2 state, but 3d9 4s1 is lower in energy than 3d8 4s2. So, what is this table listing? The lowest state or which is lower 3d8 4s2 or 3d9 4s1? I hate J-J coupling. I should note that there is no dispute about the data, both experiment and theory agree. AManWithNoPlan (talk) 15:33, 6 March 2011 (UTC)
If this table assumes L-S coupling, then the correct answer is 3d9 4s1, since the answer for that question is the average of all J states. See: [2]. AManWithNoPlan (talk) 15:36, 6 March 2011 (UTC)
The NIST table does assumes LS coupling and specifies the J-level; the lowest level is 3d8(3F) 4s2 3F, J=4. Averaging over J levels is equivalent to neglecting spin-orbit coupling. Although since Scerri lists configurations without the values of L and S, I assumed he was also averaging over states with different L and S, which is equivalent to neglecting the interactions which cause multiplet splitting.
From the experimental spectra which include all physical effects (electron correlation, multiplet splitting, spin-orbit coupling, relativity etc.), the true ground state of the nickel atom is 3d8(3F) 4s2 3F, J=4. This is the implicit basis of the textbook choice of 3d8 4s2 as configuration, whereas the papers which choose 3d9 4s1 are based on a model which neglects at least one interaction.
As for agreement between theory and experiment, this depends on the level of theory. Scerri quotes averaged Hartree-Fock values which actually predict that the average for 3d8 4s2 is lower, which is why he says that the calculations give an incorrect ground state. (He mentions that this is true for relativistic Hartree-Fock calculations, but his values show that it is also true for nonrelativistic Hartree-Fock, so relativity actually has no effect on the conclusion here). He adds that the calculations can be improved by adding extra terms.
Anyway I agree with 130.126.92.40 that the table layout imposes brevity, so I agree with just listing the two configurations and adding the word disputed. An alternative word might be near-degenerate. We can explain further in the Nickel article, which already mentions that both configurations have been proposed, although the explanation in that article needs a few corrections. Dirac66 (talk) 14:49, 7 March 2011 (UTC)

## Section Other exceptions to Madelungs rule

I am confused. Is the above section showing ground states or not?? For example it says (as one example amongst many) that the ground state of Neodymium is [Xe] 6s2 4f4, (I am assuming it is the ground state as it says earlier in the article "The remainder of this article deals only with the ground-state configuration, often referred to as "the" configuration of an atom or molecule.") In another article Electron configurations of the elements (data page) ; it gives this as the ground stae neodymium : [Xe] 4f4 6s2.

My second point is that the electron configs of T. metals and lanthanides are problematic. The aufbau principle says that for exampe 4s is filled before 3d and yet when T. Metals ionize they lose 4s electrons first, this so called "paradox" is mentioned in this article but I think the "resolution / explanation" given is obscure to say the least. Wouldn't a discussion on the real spectral evidence with say scandium as a simple example, with the configs of Sc3+,[Ar]; Sc2+, [Ar]3d1; Sc+, [Ar]3d14s1; Sc0, [Ar]3d14s2 to show how the electron config. of Scandium is actually built and why the 4s electrons are the highest energy.Axiosaurus (talk) 18:43, 14 February 2014 (UTC)

For Nd, the answer is that [Xe] 6s2 4f4 and [Xe] 4f4 6s2 mean exactly the same thing, so there is no real disagreement between the two articles. Both notations describe the same orbital occupancies and it doesn't matter in what order we write the orbitals. In particular we cannot deduce from these notations which orbital is easiest to ionize and what is the configuration of the Nd+ ion. This point should be included in the article, probably using a lighter atom than Nd as example.
For aufbau, the point is that Sc2+ and Sc+ do not have the same configuations as the isoelectronic neutral atoms K and Ca respectively. We do mention now that There is no special reason why the Fe2+ ion should have the same electron configuration as the chromium atom, given that iron has two more protons in its nucleus .... Perhaps we can be clearer.
Finally you mentioned first the above section on nickel, which is a special case and requires that we distinguish carefully between configurations and states. For most atoms, the lowest-energy configuration is well below all other configurations, and the ground state is one state of this lowest-energy configuration. The exact state is identified by various quantum numbers for orbital angular momentum and spin, as given by Hund's rules. However for nickel there are two configurations very close in energy, and the ground state is 4s2 3d8 while the lowest (average) energy configuration (sometimes called the ground state configuration) is 4s1 3d9. Perhaps this article could refer to the article on Nickel for more information - at the moment we just give a source which is not accessible to all readers. Dirac66 (talk) 20:34, 14 February 2014 (UTC)
OK I see what you are saying. However the order of the orbitals is used ( e.g. Greenwood in his book) to describe the ground state. For Nd the config. [Xe] 4f4 6s2 is used to show that the 6s electrons are higher in energy, and get ionised first. This ordering convention should be mentioned. It is used in the Electron configurations of the elements (data page) article! I am trying hard not to get on Scerri's soap box but the aufbau principle is nothing more than a data fit algorithm and "works" well for the lighter elements showing occupation and ground state, but for the heavier elements (with a few exceptions) it just shows the energy levels that are occupied but not their relative energies. I think that theres a lot of content missing in wikipedia coverage of this area.Axiosaurus (talk) 10:39, 15 February 2014 (UTC)

## Chemistry

Is it possible to find electron configuration through BM. Aditya Chaturvedi (talk) 05:48, 30 January 2017 (UTC)

BM = Bohr magneton? The magnetic moment measured in units of Bohr magnetons can be used to determine the number of unpaired electrons, which provides information about the electron configuration. Dirac66 (talk) 03:36, 2 February 2017 (UTC)

## Typo ?

In the paragraph notation : "For example, the electron configuration of the titanium ground state can be written as either [Ar] 4s2 3d2 or [Ar] 3d2 4s2."

Should not it be [Ti] instead of [Ar] ?

No. It is argon plus more electrons.
Yes, [Ar] in square brackets means "the same configuration as Ar". I have now expanded the preceding paragraph to make this clearer for [Ne]. Dirac66 (talk) 19:40, 13 February 2017 (UTC)
I just worked on it some more. My main goal was to make sure we used and linked the key differential terminology of core electron vs valence electron (a few sentences later in the article, this distinction is discussed further). I also removed one of the two places where neon's configuration was written out explicitly (seemed redundant). DMacks (talk) 21:30, 13 February 2017 (UTC)