User talk:Axiosaurus/draft1
Oxidation state
[edit]You have done a lot of work and the result is a net improvement. One editing error is that the IUPAC rules are now included twice. A deeper flaw I think is that the IUPAC and electronegativity (EN) approaches are not really separate from each other. In my view the EN section does not really need examples, since the exceptions and extensions to the IUPAC rules ARE the examples for the EN method, so I would integrate the IUPAC and EN approaches. We could start by pointing out that IUPAC's normal rules (H +1, O -2) apply when H is bonded to a more EN element or O is bonded to a less EN element. Then we can say that the exceptions in the IUPAC statement (hydrides, peroxides) are also based on EN, as are the extensions to the rules you have listed (halogens -1 except ..., etc.)
- I agree with your points on the IUPAC and EN are not really separate, but the IUPAC definition does not include electronegativity, and that approach has been adopted and taught particularly in the US. Students taught this way I think are at a huge disadvantage. There is real divide between a rule system and the EN method, I am concerned that readers at high school level could get confused and thats why I separated the approaches so that students from different educational systems could read about their way. Let me stew on this.
- OK then, how about keeping the IUPAC section for the rules which are actually included in the IUPAC definition, and moving the non-IUPAC part starting In practise these rules are usually extended to serve as examples for electronegativity. Especially since the first three extended rules explicitly use the words electronegativity, electronegative and electropositive. I'll tentatively move this part on your draft to clarify what I mean. Dirac66 (talk) 13:08, 20 September 2013 (UTC)
- I agree with your points on the IUPAC and EN are not really separate, but the IUPAC definition does not include electronegativity, and that approach has been adopted and taught particularly in the US. Students taught this way I think are at a huge disadvantage. There is real divide between a rule system and the EN method, I am concerned that readers at high school level could get confused and thats why I separated the approaches so that students from different educational systems could read about their way. Let me stew on this.
However as well as indicating the use of EN to find oxidation states, we should also point out its major limitation (with examples?) which is that the ordering of EN is not always clear because it is not a measured quantity and there is no universally accepted scale. This is presumably why IUPAC chose to eliminate explicit mention of EN from the definitions.
As for oxidation number vs. state, I agree that they are generally two names for the same values, and I am dubious that coordination chemistry is an exception to this rule. Rather I would say that for an atom in a coordination complex there is one value of OS/ON, but that the metal-ligand rule (or oxidation number) is used instead of EN values because the metal-ligand rule is less ambiguous. So for Wilkinson's catalyst Rh is +1 whether one chooses to call it OS or ON. Surely no chemist actually considers Rh to be -5 in this molecule. Admittedly the IUPAC statement does not make this clear at all. Dirac66 (talk) 01:30, 20 September 2013 (UTC)
- My knowledge of the use of this definition is limited. However it seems to prevent any simple approach such as taking an ammine complex and assigning electrons to the nitrogen atoms on the basis of electronegativity, and coming up with very high ox states. (Werners ideas going way back) The usual definition I see in literature is the notional removing the ligands in their closed shell structure. Sorry must close off we are out shopping! Axiosaurus (talk) 10:40, 20 September 2013 (UTC)
- For a typical ammine complex such as [Co(NH3)6]3+ the Co-N bonding electrons are always assigned to N. It makes no difference whether we say this is because N is more electronegative than Co or because NH3 is the ligand. The only difference is for the exceptional case where the metal is more electronegative than the ligand binding atom, as in the Rh-P bonds of Wilkinson's complex. In this case blind use of Pauling's method would lead to absurdly negative OS, such as Rh(-5)(or -V?) in Wilkinson's complex. So the IUPAC definition says to ignore the electronegativity values and assign the Rh-P electrons to the ligand anyway, which gives Rh(I) as in all textbooks I have seen. Dirac66 (talk) 12:29, 20 September 2013 (UTC)
- Yes you are quite right and message to self I shouldn't rush posts and ensure brain is fully engaged. Yes Wilkinsons is a good example of the definition "working". One issue with the definition I have found referenced is with Mn(CO)43- following the ON coordination compound definition then we get Mn with ON -3 however this ignores back donation, which is significant, the frequency of the C-O stretch is typical of a C=O bond, so treating the bonds to Mn as double, using Pauling and Lewis diagrams, and hey presto oxidation number now +5 which is a much more comfortable answer. Adding this to the article is worth considering once the overall structure of the article is acceptable. Axiosaurus (talk) 14:38, 20 September 2013 (UTC)
- This seems a good (and needed) example for the section on spectroscopic oxidation state. All the previously discussed definitions would naively be applied for Mn-C≡O to give ON -3; the revision to Mn=C=O and ON +5 requires IR (or Raman) spectroscopic data. Best to find a reference for this reasoning though, so as not to be accused of OR. Dirac66 (talk) 20:05, 20 September 2013 (UTC)
- Yes you are quite right and message to self I shouldn't rush posts and ensure brain is fully engaged. Yes Wilkinsons is a good example of the definition "working". One issue with the definition I have found referenced is with Mn(CO)43- following the ON coordination compound definition then we get Mn with ON -3 however this ignores back donation, which is significant, the frequency of the C-O stretch is typical of a C=O bond, so treating the bonds to Mn as double, using Pauling and Lewis diagrams, and hey presto oxidation number now +5 which is a much more comfortable answer. Adding this to the article is worth considering once the overall structure of the article is acceptable. Axiosaurus (talk) 14:38, 20 September 2013 (UTC)
- For a typical ammine complex such as [Co(NH3)6]3+ the Co-N bonding electrons are always assigned to N. It makes no difference whether we say this is because N is more electronegative than Co or because NH3 is the ligand. The only difference is for the exceptional case where the metal is more electronegative than the ligand binding atom, as in the Rh-P bonds of Wilkinson's complex. In this case blind use of Pauling's method would lead to absurdly negative OS, such as Rh(-5)(or -V?) in Wilkinson's complex. So the IUPAC definition says to ignore the electronegativity values and assign the Rh-P electrons to the ligand anyway, which gives Rh(I) as in all textbooks I have seen. Dirac66 (talk) 12:29, 20 September 2013 (UTC)
- My knowledge of the use of this definition is limited. However it seems to prevent any simple approach such as taking an ammine complex and assigning electrons to the nitrogen atoms on the basis of electronegativity, and coming up with very high ox states. (Werners ideas going way back) The usual definition I see in literature is the notional removing the ligands in their closed shell structure. Sorry must close off we are out shopping! Axiosaurus (talk) 10:40, 20 September 2013 (UTC)