Template talk:Periodic table (valence)

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I stumbled across this page at random - just wondering why its a sub-page - subpages arent used any more at wikipedia usually? -- Astrokey44|talk 03:10, 24 March 2006 (UTC)

Moved it from Valence (chemistry)/Table to Template:Valence table. Subpages in main namespace are disabled. --Ligulem 19:00, 6 January 2007 (UTC)

Could someone correct the typo on the title? After "Periodic table", the word in parenthesis should be "valence", not "valance". —Preceding unsigned comment added by 86.92.226.147 (talk) 18:56, 10 January 2008 (UTC)

There should be some serious referrencing in this page, especially for the 7th period! Nergaal (talk) 01:28, 26 January 2009 (UTC)

Liquids[edit]

Hello,

Caesium, francium, gallium, rubidium are liquid at room temperature. The atomic number should be green. Yann (talk) 10:53, 3 June 2009 (UTC)

Only if your room is really hot. Usually "room temperature" is taken to mean 25 degrees Celsius, which is slightly below the melting points of these elements. --Itub (talk) 00:25, 5 June 2009 (UTC)

Changed much[edit]

Yeah, that seems weird (valence of nine for rhenium, two for hydrogen, five for carbon and so on). But that suits IUPAC definition. If disagree, I may explain--R8R Gtrs (talk) 20:18, 16 November 2010 (UTC)

You may not explain - you must cite (and by this, I mean, cite a source that says "the valence of atom A is x", not "there exists a compound AFx or AHx"; I think you're misinterpreting the IUPAC definition)!
The threshold for inclusion in Wikipedia is verifiability, not truth; that is, whether readers can check that material in Wikipedia has already been published by a reliable source, not whether editors think it is true.
http://en.wikipedia.org/wiki/Wikipedia:Verifiability
Wikipedia does not publish original research. The term "original research" refers to material—such as facts, allegations, ideas, and stories—not already published by reliable sources. It also refers to any analysis or synthesis of published material to advance a position not advanced by the sources.
http://en.wikipedia.org/wiki/Wikipedia:No_original_research
Case in point: a 3-center bond counts for only 1 valence, not 2, since only one electron of the parent atom participates in the bond, not 2. Therefore, the example of HF2(-) cannot be used to argue that H has a valence of 2. Neutral H has only one electron, and assigning a valence higher than the number of electrons is nonsense. This whole table looks like it has been put together by a hardcore fan of theoretical research into hypervalent molecules and is all but useless from a practical chemical point of view.
I'm going to put up an "original research" template. I'm not saying I am all knowing and this table is all wrong, but at the very least, citations are needed. A lot of them. Let me start with one: J. Chem. Educ., 2006, Vol 83, p 791. It says that the valence of B in BH4- is 3 and the valence of C on CH5+ is 4, in agreement with my observation that a 3-center bond only counts for 1 valence.
OneAhead (talk) 00:42, 28 December 2010 (UTC)
In fact, you can say the H- ion has a valence of two, not H. However, H- is not an element and is not in the periodic table.--Wickey-nl (talk) 16:53, 28 December 2010 (UTC)
While H- does have 2 valence electrons, I don't think it can be said to have a valence of 2. The two electrons form a full 1s shell (just like helium) and to form two covalent bonds, the second electron has to promote to the 2s shell (there is no 1p), which is energetically too expensive to be compensated by any bond energy. Consequently, there are no compounds in which hydrogen has a formal negative charge (on HF2-, the negative charge is delocalized over the two fluorines), just like there are no Helium compounds (Despite what the table says, Helium has a valence of 0 http://en.wikipedia.org/wiki/Helium#Compounds ).
But this aside, your point that ions are not elements and cannot be used to assess the valence of an element is valid and relevant. The more I look at this table in its current version, the more I get convinced that it's utterly incorrect, and I feel sick thinking of all the students that get thoroughly confused by looking up "Valence" on Wikipedia. If you look at the page history http://en.wikipedia.org/w/index.php?title=Template:Periodic_table_%28valence%29&action=history , all this damage was done by one well-meaning individual applying his or her incorrect interpretation of the IUPAC definition on (often unstable) molecular ions he or she looked up (and making incorrect extrapolations "guessed from periodic trends"). If nobody objects within a week, I'm going to revert to the version of the 17th of October. OneAhead (talk) 22:04, 31 December 2010 (UTC)

First of all, I'm that "one well-meaning individual" and I'm not going to argue forever, if I'm wrong, just explain. I won't reject all you say, and, like you, just want it all in the best way for Wikipedia. All the compounds I've mentioned are in Wikipedia; also, about valence, from Valence (chemistry) (reference can be found there):

The International Union of Pure and Applied Chemistry (IUPAC) has made several attempts to arrive at an unambiguous definition of valence. The current version, adopted in 1994: The maximum number of univalent atoms (originally hydrogen or chlorine atoms) that may combine with an atom of the element under consideration, or with a fragment, or for which an atom of this element can be substituted.

If that doesn't mean "the maximum number of one-bond-forming atoms that can be bonded to this element atom", then I'm sorry and then what does that mean? Also, helium forms metastable H-He-F, like mentioned in Neon#Compounds (there's a reference!). Also, bifluoride is F-H-F, so that two fluorines bonded to a hydrogen. This, if I got the definition right, leads to valence of 2 for H. Also, all that is just guessed from "periodic trends" is removed a long ago. Also, citing a source that says "the valence of atom A is x" may not be it. Seriously, current definition is applied in 1994 and isn't used mostly; I can give references to the compounds, but you say that's not what's needed.

And, finally, back to the definition: if that doesn't mean what I think it does, I want to be explained (not just said I'm wrong) and if I'll feel I was wrong then I will revert all my edits myself, only leaving 4 to mercury.--R8R Gtrs (talk) 14:03, 16 January 2011 (UTC)

  • The IUPAC definition is not clear on whether compounds with very low stability count towards defining an element's valence or not, but most textbook sources do not consider them.
  • You translated the IUPAC definition of "univalent" to "one-bond-forming". I think I can agree with that, but then the bonds in F-H-F(-) (don't forget the charge!) are not simply "one bond each". There are at least 3 different ways of describing this molecular ion:
    • single resonance structure with one covalent bond and one hydrogen bond
    • fractional bond orders - two bonds with bond order 0.5 each
    • one 3-center 4-electron bond
All of these three descriptions yield a valence of 1 for hydrogen. And that's ignoring Wickey-nl's (correct) observation that ions cannot be used to define an element's valence...
  • Have you even looked at that the reference for H-He-F you're referring to? It says "In computational studies, Wong found HHeF to be a bound species presumably capable of being synthesized, although Lundell et al. were cautious about the ability of this compound to exist." I'm a computational chemist myself an have many times seen species that clearly don't make sense arise from my quantum chemical calculations. There are a large number of non-trivial pitfalls in quantum chemistry, and as far as I am concerned, Wong et al. are probably reporting an artifact and Lundell et al. are justly cautious about this.
My personal opinion aside:
    • Wong's result is a very clear-cut example of original research and does not belong in Wikipedia.
    • Not only is it original research, it is being contested!
    • Following Wikipedia's definition of "original research", by applying the IUPAC rules on compounds you find on the internet, you're performing original research yourself. You're saying citing a source that says "the valence of atom A is x" may not be it but citing a source that says "the valence of atom A is x" is exactly it!
  • You also say "Seriously, current definition is applied in 1994 and isn't used mostly." You're spot on there - I haven't ever seen a chemistry textbook applying the IUPAC definition on the kind of compounds you're looking at. In fact, valence is an obsolete concept that is not rigidly defined in the face of modern chemistry. Nevertheless, it is still a very valuable mental tool in thinking about the octet rule in organic chemistry, and that's how it's presented in textbooks. This is wikipedia, not "current opinions in theoretical research on hypervalent chemistry"; let us stick to the textbooks (and J. Chem. Educ.) rather than trying to apply a disused IUPAC definition to compounds it was never meant to cover.
  • Also see http://en.wikipedia.org/wiki/Talk:Valence_%28chemistry%29#Simple_valence_rules_vs._modern_bonding_theory and http://en.wikipedia.org/wiki/Talk:Valence_%28chemistry%29#expert_needed
OneAhead (talk) 01:43, 29 January 2011 (UTC)

I'm convinced by anything said here and below, you're definitely right and I was wrong, I admit it. Sorry for it all. Reverted, hope that to be OK. I'll only mark argon as with valence of 2, and mercury - 4, OK (per HArF and HgF4, both with even Wikipedia articles)? However, wait, I won't. Also, I'm not sure the heaviest elements have any valence, since that'd also be original research, wouldn't it?

So I've just reverted first 84 elements. Again, sorry. Hope you all understand I didn't mean anything bad (that's, at least, should be temporary, if there are still big issues to discuss)--R8R Gtrs (talk) 19:49, 10 February 2011 (UTC)

No problem - It makes me happy that you're open-minded about it and that my initial critique, which probably was a bit overly aggressive, doesn't end up starting a hurtful and time-consuming "is not - is too" discussion. OneAhead (talk) 20:57, 12 March 2011 (UTC)

Delete?[edit]

Valence is not defined. Better would be to show minimum and maximum oxidation states, if this template would be usefull at all. The table will never be completely correct, nor will it be possible to account for all claims. Therfore, this is a good deletion candidate.--Wickey-nl (talk) 14:28, 7 January 2011 (UTC)

Although not rigidly defined, valence is still a very valuable tool in education and in writing down reaction mechanisms in organic chemistry. If you go back in the history of this template, the version of the 17th of October is one I could perfectly live with - it reflects the "old-fashioned" concept of valence as used de facto in organic chemistry. If I have to choose between the current version of the table and deletion, it's deletion hands down, but reverting it to the 17th of October would be much preferable because then
  • it's still there for people with educational/historical interest in the concept of valence
  • the hard work of people who put together the various versions of this table is not permanently lost - in fact, if we can't reach agreement of what to do with the table, we could unlink it from pages such as Valence (chemistry), and leave it here in its orphaned state until a consesus is eventually reached.
OneAhead (talk) 01:59, 29 January 2011 (UTC)
The value of the valence concept is not disputed, nor the faithful work. But it is questionable to place a table that is principally unreliable. Moreover you can ask whether people will use this table as a reference. Who needs the theoretical maximal valence? The original form of the table as normal article page will be more appropiate, along with some additional information; this also because of the doubtful value as reference in a template.--Wickey-nl (talk) 11:18, 29 January 2011 (UTC)
Here is my opinion, as requested by OneAhead on Talk: Valence (chemistry). The current table has many non-standard values which should be removed. The IUPAC definition cited is unfortunately very brief and ambiguous, with no examples provided, and it is evident (if only from the above discussion) that several interpretations are possible. The current table appears to be based on the assumption that for a given element, we are to consider any species (molecule or ion) ever reported, no matter how exotic. My suspicion is that IUPAC had in mind only common neutral molecules; the word maximum would apply to cases where an element forms common neutral molecules with different number of bonds such as PF3 and PF5.
No, I have no source which explicitly shows that this was IUPAC’s intention, but neither has anyone given a source that explicitly cites IUPAC’s preferred valences to be 2 for H, 2 for F and 5 for C. Therefore Wikipedia should not be presenting this disinformation to readers.
So we can do one of two things – delete the table entirely, or produce an acceptable version. I think that values of valence are historically important, and still useful in organic chemistry especially, so a table is useful. However we should only use values given explicitly in standard sources such as university chemistry texts, which normally assume neutral molecules. Also, it is probably better not to present a unique (or maximum) value for each element, but instead we can list the common values, as (3, 5) for P. This would require that we write all the numbers instead of using a colour code. Rare values can be placed in parentheses as in some books. And if there are no sources for the valences of some newer elements, just leave these elements blank in the table. Dirac66 (talk) 01:47, 30 January 2011 (UTC)
Fully agree with both deleting and rewriting.--Wickey-nl (talk) 14:59, 30 January 2011 (UTC)
Sorry for my late reply. I want to thank Dirac66 for their valued explanation; I fully agree with this interpretation of the IUPAC rule and with using values given explicitly in standard sources such as university chemistry texts. As for the "delete" versus "produce an acceptable version" discussion, I'm in favor of the latter option. R8R Gtrs already restored the table, removing all numbers based on original research, ions and exotic species. This is a good starting point for further fine-tuning, such as listing a number of common values, with rare values in parentheses. As far as I am concerned, the current coloring by highest value can remain while introducing numeric values; the colors reveal nice trends and it's never bad to show information in more than one way (provided that it doesn't get cluttered). OneAhead (talk) 20:57, 12 March 2011 (UTC)