Talk:Hund's rules

message: This is an atrocious page as of 21April, 2014, for learning the Hund's Rule. It was written by someone who has little idea of teaching science to others.
If you already know Hund's rule, then perhaps you can pick up some detail or nuance from the page. But the page should be rewritten so that someone who never heard of Hund's Rule can learn what it is.
Every textbook in beginning chemistry provides a easy understandable version of Hund's rule, and that is what Wikipedia should start its "Hund's Rule".
So that the first chapters should be the easy version and then take the existing write up and class it all into the advanced Hund's Rule chapters.
Many Wikipedia science entries suffer from authors who know only how to talk the subject as if they were talking to people who already know it. It is the author's who write the subject for those who know nothing about it that is the most valuable write up and should appear first, and then later on in  a chapter, devoted to the advanced discussion of the topic.
So, Wikipedia needs very much to make science discussions not so atrocious.
Archimedes Plutonium wrote this review.  — Preceding unsigned comment added by 198.228.228.153 (talk) 06:54, 21 April 2014 (UTC)
thread_title: writing science topics in Wikipedia

message: I noted this on the page for Term_Symbol as well, but perhaps this is a better place. On the page for Hund's_Rules, it states that they can only be used to determine the ground state, 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 07:00, 21 September 2006 (UTC)
thread_title: Excited states

message: "For atoms with less than half-filled shells, the level with the lowest value of J \, lies lowest in energy. Otherwise, if the outermost shell is more than half-filled the term with highest value of J \, is the one with the lowest energy." This sentence is confusing me for the exactly half filled case. It says 'less than half filled shells...otherwise...more than half filled' what about half filled shells? This is made more confusing in the body, where it says 'The value of \zeta (L,S)\, changes from plus to minus for shells greater than half full.' Xaerocool 08:20, 27 October 2006 (UTC)
thread_title: Half-filled shells

message: A mention perhaps about the case of Zinc, where subshells are full (Example 2?) --sigs  —Preceding unsigned comment added by 82.130.14.161 (talk) 22:23, 18 October 2007 (UTC)
thread_title:  what about when the subshells are full 

message: Surely this should say that term energy is lowest when S is maximised. At the moment it says that term energy is highest when S is maximised, which I believe to be incorrect.  <
I have now changed "highest" to "lowest".  Dirac66 (talk) 03:38, 9 March 2008 (UTC)
thread_title:  There is an error in rule 2 

message: As far as I was aware there are only 3 Hund's Rules, and these appear as 2, 3 and 4 on the page. I have no idea what rule 1 is going on about, and the explanation given for it makes little sense to me - it mentions repulsion between protons, which has nothing to do with electronic configuration. 
If I was to edit the page I'd remove all mention of this phantom 1st rule that is currently there, and re-number the remaining 3 rules accordingly.
Problem with the explanation given for rule 2 (which would be rule 1 if I editied the page as suggest above) are in the 2nd paragraph;
It is often stated that this is the highest energy atomic state because it forces the paired electrons to reside in different spatial orbitals, and this results in a larger average distance between the two electrons, reducing electron-electron repulsion energy. But, in fact, careful calculations have shown that this explanation can be wrong, at least for light systems
To start with, the state with maximised paired electrons is the lowest energy state, not the highest. My understanding is that this arises from the Fermi Hole in the wavefunction of paired electrons reducing electron-electron repulsion. The article appears to disagree with me here;
...in fact, careful calculations have shown that this explanation can be wrong, at least for light systems.
but no citation is given for this statement.
Krusader86 (talk) 15:53, 28 November 2007 (UTC)
thread_title:  Confusion about rule #1, and problems with rule #2 

message: Yes, Hund proposed 3 rules and not 4. See for example Miessler and Tarr "Inorganic Chemistry" (2nd edn 1999), pp. 358 and 360.
The current (9 Mar 2007) "first rule" in the article is spurious and was inserted by a very confused editor (or vandal?) on 4 November 2007.  
Prior to that edit, the following statement was cited as the "first rule":
Full shells and subshells do not contribute to total S, the total spin angular momentum and L, the total orbital angular momentum quantum numbers. 
This is in fact a true statement, but is usually presented as a preliminary statement and not as the "first rule". 
I will renumber the rules, and reinsert the correct version of the preliminary statement.  Dirac66 (talk) 04:21, 9 March 2008 (UTC)
thread_title: Spurious rule #1

message: If the average separation between two orbitals is increased, the screening effect of one electron on the other will be reduced. So the two "different" explanations given for Hund 1 are really the same. That is, unless the modern explanation has voodoo which makes it so that the screening effect from inner shells is somehow enhanced when the outer electrons are in separate orbitals! I think the reason for the explanatory quibble is only because the hartree-fock method includes the interaction between electrons mainly in the form of the self-consistent potential, so that the greater distance when the electrons are in separate orbitals translates to a larger self consistent potential, and therefore to "greater screening", and this is the dominant reduction. But a greater screening is a reflection of the greater average distance between the electrons.Likebox (talk) 22:27, 21 September 2009 (UTC)
thread_title:  Screening vs. Separation 

message: The body of the article needs citations to specific articles in the References. If a whole paragraph can be attributed to a single source, a citation at the end of the paragraph is enough. I have added two citations as an example. RockMagnetist (talk) 01:44, 24 September 2010 (UTC)
replies: text: Yes, in-line references are better, though more work to do. I have now changed the format (and the year) of your in-line reference to Levine, since clicking on your "Levine 2006" did not produce the book title and pages. I also converted the Engel-Reid and Miessler-Tarr references (which I had added some time ago) into in-line references at an approprate point in the text. Can't check the Woodgate reference since I have never seen this book.  Dirac66 (talk) 02:54, 24 September 2010 (UTC)
thread_title:  Citations needed 

message: The traditional explanation of Hund's rule 1 is that electrons with same correlate their motion by remaining far apart from each other  and hence minimize the repulsions . Hence the term with higher multiplicity shall have lower energy. 
However this explanation proves wrong . It has been found, probability that the two electrons are very closer is small for triplet term than for singlet term. But at the same time using exact wavefunction, it turns out that two electrons in triplet state are very far, is also very less. Average distance between two electrons in triplet term is less comparable to singlet. So repulsions in triplet state are stronger than in singlet state, yet triplet state is lower in energy than singlet. 
The reason behind this strange result is that in triplet state there is more attraction of electron clouds towards nucleus compared to singlet state. The occupancy of two electrons in two orbitals with same spin lead to Paulis  repulsion which causes the two electrons to make average angle between the radius vectors larger for triplet state than singlet. This reduces the shielding effect and hence stabilize triplet state more than singlet.
References:
R.E.Boyd, Nature, 310, 480(1984).
J.Katriel and R.Pauncz adv.Quantum Chem., 10,143 (1977).
I.Shim, Theor.Chim.Acta, 48, 165(1978). Aejaz Ul Bashir (talk) 07:01, 22 June 2020 (UTC)
replies: text: Yes, this is exactly the second explanation given in the article, starting with the words "However, accurate quantum-mechanical calculations ...". The version in the article is a summary of that given in Levine's book, which cites the same 3 references you have cited here. So I am not certain what you think you should be changed in the article. Dirac66 (talk) 20:26, 22 June 2020 (UTC)
thread_title:  Rule1