Talk:Term symbol

Hund's rules and excited states

If anyone happens to read this, on the page for Hund's_Rules, it states that they can only be used to determine the ground states, not to order the excited states by energy. However, on the Term_Symbol page it seems to use Hund's Rules for exactly this. I don't know enough about the subject to know where the error lies, but there certainly appears to be an inconsistency at present. --Westm 06:58, 21 September 2006 (UTC)

I have now rewritten both articles to clarify this point. Briefly, the rules can be used to determine the lowest-energy state of any given configuration, ground or excited. They should not however be used to order the states other than the lowest for each configuration. See examples at Hund's rules#Excited states. Dirac66 (talk) 20:20, 22 June 2008 (UTC)

Needs to be rewritten

I think this page needs to be rewritten, and made clearer and simpler.

My thesis is on computational and quantum chemistry, and I could honestly not understand and follow the logic of the page, nor find the information that I was looking for.

Doktor Erik (talk) 18:39, 6 June 2008 (UTC)

Can you be more specific about the improvements you would suggest? What information were you looking for? What needs to be simplified or added?

One possibility would be to just retain sections 1 and 2 which explain the meaning of the term symbols and all the quantum numbers. The problem of finding all term symbols for a given configuration is rather complicated for Wikipedia, both by Slater's method and by group theory, and could be replaced by a brief mention with an appropriate literature reference. Or would you prefer to keep at least one method for solving this problem and explain it better?

Or do you have something else in mind? Dirac66 (talk) 02:29, 7 June 2008 (UTC)

Alternative method using group theory is incomplete

The alternative method using group theory as presented is incomplete. You can only use the rules presented here to work out terms with at most two electrons (or holes) per orbital. Furthermore, it is unclear wether using group theory for three or more electrons in an orbital is simpler than the method of counting microstates. In the discussion above, this is referred to as Slater's method. If this method can indeed be attributed to Slater, it would be great to have a reference. For example, for a 2p³ configuration

Γ^(1/2) × Γ^(1/2) × Γ^(1/2) = Γ^(3/2)(A) + 2Γ^(1/2)(E)

P × P × P = S(B) + 3P(A+E) + 2D(E) + F(A).

where A,B,E are the irreducible representations of the S₃ permutation group. Since the overall symmetry with respect to this group must be B, the only allowed configurations are ⁴S, ²D, and ²P. The catch is that assigning the different terms of (Γ^l)ⁿ and (Γ^s)ⁿ to irreducible representations of S_n is still a fairly significant counting problem for n>2. Furthermore, this discussion almost certainly exceeds the scope of Wikipedia. 128.146.35.211 (talk) 22:17, 4 November 2011 (UTC)

I have now noted the limitation to two electrons (holes) at the beginning of the section. As you say, the method for 3 or more electrons (holes) is too complex for Wikipedia. We could, however, refer the general case to a suitable reference, if you have one. Dirac66 (talk) 00:23, 5 November 2011 (UTC)

Small error in the text

The article says: “S is the total spin quantum number. 2S + 1 is the spin multiplicity: the maximum number of different possible states of J for a given (L, S) combination.”

My concern is with this part “2S + 1 is the spin multiplicity: the maximum number of different possible states of J for a given (L, S) combination.”

2S + 1 is the maximum number of different possible states of J for a given (L, S) combination only if L is greater or equal to S, i.e. L≥S. Otherwise the maximum number of different possible states of J is 2L+1. Please see L.D. Landau and E.M. Lifshitz "Quantum Mechanics. Non-relativistic Theory" & 66 "Atomic energy levels" for reference. — Preceding unsigned comment added by Pauk1234 (talk • contribs) 10:47, 7 February 2016 (UTC)

Yes, you are correct, thank you. I had recently made the same correction to the article on Multiplicity (chemistry). I have now corrected this article also. Dirac66 (talk) 13:14, 7 February 2016 (UTC)

Incorrect term symbol for Copper

The term symbol should be S rather than D, as the d orbital is full and the s orbital is half full. Mearley13 (talk) 02:54, 18 January 2019 (UTC)

Yes, you are right. For Cu with configuration [Ar] 3d¹⁰ 4s¹, the complete term symbol should be ²S_1/2, not ²D_1/2 and the short term symbol should be S, not D. The same corrections should be made for Ag and Au.

I would make the corrections, but I cannot find the source code which needs changing. It seems to be part of a template within a template (??). Can anyone else find it? Dirac66 (talk) 16:18, 18 January 2019 (UTC)

I think fixed, now. Thanks to user:Double sharp.SBHarris 07:17, 23 January 2019 (UTC)

Calling all periodic table drawers

Thanks to all who have participated in the term symbol element list, but it should be collapsible. Could somebody PLEASE make up a simple periodic table with nothing but element symbols (or names) and the ground state term symbol? The list table in the article now is long and messy, it repeats information from elsewhere, and the regularities in it are mostly hidden (just as in a list of elements, which this is). Term symbols, after all, depend on electron configation, and vary periodically. Not QUITE as regularly as columns in the periodic table (some f and d blocks change) but ALMOST (as noted in the article, s and p blocks consist of columns that are uniform in term symbol).SBHarris 07:02, 25 January 2019 (UTC)

See {{Periodic table (term symbol)}}. OK? -DePiep (talk) 09:25, 25 January 2019 (UTC)

Great job, DePiep! See the regularities and almost-regularities in columns (caused by mostly-relativistic changes in electron-configuration in the unclosed outer shells). Isn't that interesting? SBHarris 02:49, 26 January 2019 (UTC)

Yes very intresting. I shifted the texts (element and term symbol) left/right so that this vertical regularity (=periodicity!) shows out more. Sorry it took some many months. Just a question: is there anything to say about the lanthanides and actinides re term symbols? No regularity at all! Just a bag of elements (is why they have no group number anyway: they don't have group behaviour). -DePiep (talk) 09:11, 26 January 2019 (UTC)

The periodic table format is indeed much better, since it shows the elements arranged in a natural way instead of in one boring column. Actually there were 2 columns, but the second (quantum number L only) was redundant and I am glad you have now suppressed it.

With this format I was able to spot an error that I missed before: Es(Z=99) cannot be a quintet since it has an odd number of electrons. I would guess it is ⁴I_15/2 like Ho(Z=67), but please check before making the correction. Which brings up the point that the article should give a reliable source for all the ground state term symbols. I suggest the NIST tables which are open access. The NIST website has been down for a few weeks due to the American political situation, but there is now a notice saying it will be back up on Monday Jan.28.

As for the lanthanides and actinides, presumably the differences in ground states for the first 4 columns are due to the fact there are several states close in energy so that the exact order is perturbed by adding another closed shell. For example, since Ce is ¹G₄ and Th is ³F₂, it will be interesting to note for comparison the energies of the excited states Ce(³F₂) and Th(¹G₄). These energies can be found in the NIST tables.Dirac66 (talk) 19:18, 26 January 2019 (UTC)

Thanks Dirac66 for this very nice & clarifying & helpful reply. Let me note that in the grand Periodic Table talks (WT:ELEMENTS), 'Term symbols' now have an entry here.

Data errors for example re ₉₉Es you mention: go bold, change {{Infobox element/term-symbol}}, add RS to Es I say.

re Ln's and An's: see WP talk elements/this. In the f-block (those nasty Ln's and An's, they don't behave) there are 5/14 f-block irregulars. Also, in the d-block there are 5/10 irregulars. FWIW. (My aim is to make 'Term symbols' useful for the periodic table).-DePiep (talk) 21:53, 26 January 2019 (UTC)

I have now added the NIST tables as the authoritative reference for the elements with experimental data. (It will be available until Feb.15 at least; after that it depends on American politics.) The notes on the table are for only a few elements, mostly the heaviest elements with predicted data.

I also checked the NIST term symbols for all the elements which depart from periodicity, and I believe that Es (einsteinium) is the only error remaining after DePiep corrected Cu, Ag, Au as requested above. But I still cannot find the source code to modify Es. Could you please also change the multiplicity (=2S+1) for Es from 5 to 4? Dirac66 (talk) 03:57, 30 January 2019 (UTC)

Dirac66 I've read this, not much time today, later more. Element data can be edited in {{Infobox element/term-symbol}} (this data link is also in {{periodic table (term symbol)}}'s documentation). Go ahead. I will add the NIST link once for all, and the exception references, somehow. (BTW, that NIST block is not a paywall ;-) ). -DePiep (talk) 07:44, 30 January 2019 (UTC)

The exception sources can be added to the element data like this: Es RS. -DePiep (talk) 07:49, 30 January 2019 (UTC)

OK, I have changed Es. My problem was that I had tried to edit the template using the line Template documentation: view edit history purge, which didn't show the required source code. I now realized it just required Edit this page, like any other page.

In a second edit I added the NIST source on the Es line. The formatting or placement for this cite could be improved. Dirac66 (talk) 12:09, 30 January 2019 (UTC)

I have now reverted the second edit, as the cite is already in the paragraph preceding the table. It was confusing to have Es as the only element with a cite in the actual periodic table. Perhaps you can find a better way to insert the NIST cite in a different place for all the elements, not just Es. Dirac66 (talk) 13:16, 30 January 2019 (UTC)