Talk:Oxidation state

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Random comments at the top[edit]

A link to a IUPAC technical report entitled "Toward a comprehensive definition of oxidation state" has been added near the top and again near the end where the IUPAC project and the reasons for its initiation were mentioned. Mcardlep (talk) 16:11, 20 June 2014 (UTC)

Just seen new post of oxidation state. Going to attempt to combine them... user:sodium

Attempt completed. The two articles are displayed below, in case I have made any errors or left out text. I did not include some of the bottom of oxidation state as it was not directly relevant, having been taken out of the electrochemistry article (actually some of the text was written by me!) user:sodium


(former oxidation state):

Oxidation state (also referred to as oxidation number) is a convenient conceptual aproximation when working with complex electrochemical reactions. It eases tracking the electrons and verifying that they have been conserved when expressing complex half reaction equations involved in oxidation-reduction reactions.

The oxidation state of an ion is the number of electrons it appears to have compared to its neutral state (which is defined as having an oxidation state of 0). If an atom or ion donates an electron in a reaction its oxidation state is increased, if an element accepts an electron its oxidation state is decreased.

The following rules define oxidation number:

1.) The atom with the greater Electronegativity of disimiliar atoms sharing an electron is counted as receiving the electron.

2.) Identical atoms sharing an electron are each credited with one/half of the electron.


For example when sodium (electronegativity of 0.9) reacts with chlorine (electronegativity of 3.0), sodium donates one electron and gains an oxidation state of +1. Chlorine accepts the electron and gains an oxidation state of -1. The sign of the oxidation state (positive/negative) actually corresponds to the value of each ion's electronic charge. The attraction of the differently charged sodium and chlorine ions is the reason they form an ionic bond with each other.

The loss of electrons of a substance is called oxidation, and the gain of electrons is reduction. This can be easily remembered through the use of the mnemonic, OIL RIG: Oxidation Is Loss Reduction Is Gain. The substance which loses electrons is also known as the reducing agent (reductant,) and the substance which accepts the electrons is called the oxidising agent (oxidant.)

A reaction in which both oxidation and reduction is occuring is called a redox reaction. These are very common; as one substance loses electrons the other substance accepts them. Redox reactions are the basis for ionic bonding.

Despite the name, an oxidation reaction does not necessarily need to involve oxygen. In fact, even fire can be fed by an oxidant other than oxygen: Fluorine fires are often unquenchable, as fluorine is an even stronger oxidant (it has a higher electronegativity) than oxygen.


(former oxidation number):

The oxidation state or oxidation number is defined as the sum of the negative and positive charges in an atom i.e., the number of electrons it has accepted or donated.

Atoms are considered to have oxidation numbers of zero, meaning that they are electrically neutral. The positive protons in the nucleus balance the negative electron cloud surrounding it, there being equal numbers of both. If an atom donates an electron it has more protons than neutrons and becomes positive. This ion is said to have an oxidation number of +1. Conversely if an atom accepts an electron it becomes negatively charged, gaining an oxidation number of -1.

Oxidation numbers are denoted in chemical names by bracketed roman numerals placed immediately after the relevant element. For example, an iron ion, with an oxidation of +3 is expressed as iron (III). Manganese with an oxidation state of +7 present in manganese oxide is given the name manganese (VII) oxide. The motive for placing oxidation numbers in names is only to distinguish between different compounds of the same elements. The actual charge (positive/negative) of the ion is not expressed because it is not necessary for this purpose.

In chemical formulas, the oxidation number of ions is placed in superscript after the element's symbol. For example, oxygen (II) is written as O2-. Oxidation numbers of neutral numbers are not expressed. The following formula describes the element I2 accepting two electrons to gain an oxidation number of -2.

I2 + 2e- -> 2I- 

Sometimes it is not immediately evident what the oxidation number of ions in a molecule are from its molecular formula. For example, given Cr(OH)3, no oxidation numbers are present yet it is clear that ionic bonding is occuring.

There are a number of rules that can be used in determining an ions atomic number:

  • The oxidation number of (neutral) atoms equal zero.
  • In neutral molecules, the sum of the oxidation numbers adds up to zero.
  • Fluorine always has a -1 oxidation number within compounds.
  • Oxygen has an oxidation number of -2 in compounds, except (i) in the presence of fluorine, in which fluorine's oxidation number takes precedence; (ii) in oxygen-oxygen bonds, where one oxygen must neutralize the other's charge; (iii) in peroxide compounds, in which it takes an oxidation number of -1.
  • Group I ions have an oxidation number equal to +1 within compounds.
  • Group II have an oxidation number of +2 within compounds.
  • Halogens, besides fluorine, generally have -1 oxidation numbers in compounds. This rule can be broken in the presence of oxygen or other halogens, where the oxidation numbers can be positive.
  • Hydrogen always has an oxidation number of +1 oxidation number in compounds, except in metal hydrides.
See also: Electrochemistry

The problem with rules this hard coded is that there will be exceptions. For example, what's the oxidation number of the oxygen in superoxide? David M


BTW, there's a page for valency too. -- Tarquin

  • Think they should be combined? The material covered is quite different. Perhaps cross referenced? Dwmyers 18:21 Feb 18, 2003 (UTC)


Looking at this page as a whole, I think it needs a comprehensive rewrite to clarify things. The way it is currently, rules for ionic compounds are mixed in with rules for covalent compounds in a confusing way. We need some more graphics and some covalent examples, including one or two organics. I will attempt to do this when I get a chance- unless anyone else is offering... Walkerma 16:54, 11 Feb 2005 (UTC)

oxidation number[edit]

hi friends i want to know which of the following has more than one oxidation numbe 1)H2S2O4 2)H2S2O7 3)H2S2O7

I am not sure if you realize that choices 2) and 3) are the same. --132.1.207.22 (talk) 23:24, 25 March 2010 (UTC)

Should we add a separate section that list the rules for determining oxidation number in organic chemistry? For instance, to determine whether an oxidation or reduction has occurred: (the following is an excerpt from page 459 of Organic Chemistry 3rd Ed, Mark Loudon)

In organic chemistry, whether a transformation is an oxidation or a reduction is deter­mined by the oxidation numbers of the reactants and products. The calculation and use of oxidation numbers is a "bookkeeping" process that involves three steps. ... 1. Assign an oxidation level to each carbon that undergoes a change between reactant and product by the following method: a. For every bond from the carbon to a less electronegative element (including hydrogen), and for every negative charge on the carbon, assign a —1. b. For every bond from the carbon to another carbon atom, and for every unpaired electron on the carbon, assign a zero. c. For every bond from the carbon to a more electronegative element, and for every positive charge on the carbon, assign a +1. d. Add the numbers assigned under (a), (b), and (c) to obtain the oxida­tion level of the carbon under consideration. 2. Determine the oxidation number Nox of both the reactant and product by adding, within each compound, the oxidation levels of all the carbons computed in Step 1. Remember: consider only the carbons that undergo a change in the reaction. 3. Compute the difference Nox(product) — Nox(reactant) to determine whether the transformation is an oxidation, reduction, or neither, a. If the difference is a positive number, the transformation is an oxidation. b. If the difference is a negative number, the transformation is a reduction. c. If the difference is zero, the transformation is neither an oxidation nor a reduction.


Ferrous vs Ferric[edit]

I see mention of the lower oxidation state of an element, namely Iron, being referred to as Ferric(2+), while the higher oxidation state referred to as Ferrous (3+). Is it not the other way around?

203.28.115.121 03:55, 20 January 2006 (UTC)

Fixed Vsmith 12:52, 20 January 2006 (UTC)

???[edit]

does any one think this is college stuff?

137.146.167.117 21:47, 30 April 2007 (UTC)[edit]

can someone explain the term "collateral measurements?"

Format for Elementbox entries, "standard" oxidation state[edit]

The Oxidation state entries for chemical elements (using Template:Elementbox_oxistates) seem to follow a specific format. For instance for Lead: 4, 2. Both the fact that 4 is listed first and that 2 is in bold seem to be meaningful (something about "standard" states?), but I did not see it explained anywhere. I think this article might be the good place for that.

About the phrase "For an exhaustive list of the possible oxidation states of each element, see the Standard Periodic Table" does not make sense, because for instance C is listed with 4 and 2, while the article just mentioned all states from -4 to 4 are valid. This should be explained. I saw originally this was an outside link, (not responding now, but with data from http://www.chemicool.com/), which indeed mentions for C: minimum oxidation number: -4, maximum oxidation number: 4 (with a confusion betwwen ox number and ox states?).

I'm sorry I cannot help more, I'm not a chemist and this is just confusing, I hope somebody with the knowledge will help clarify.

Daniel Bonniot de Ruisselet (talk) 08:58, 26 November 2007 (UTC)

You can determine the highest common oxidation state of C or any other element on the Periodic Table by looking at the Group number. Basically the highest common oxidation state is the number of valence electrons an element has. To get the maximum, you determine the amount it needs to give up(cations), or receive(anions), to become isoelectronic with the big 8's.

Ex: highest common oxidation state for Carbon: +4; Lowest: -4. highest common oxidation state for Sulfur: +6; Lowest: -3 —Preceding unsigned comment added by 71.107.21.156 (talk) 05:15, 10 December 2007 (UTC)

Peroxide[edit]

can you please explain why O2F2 is not considered a peroxide? RolfSander (talk) 13:54, 3 September 2009 (UTC)

For the same reason that OF2 is not considered an oxide, but a fluoride. The definition given by IUPAC's glossary, as far as inorganic peroxides are concerned, is "salts of the anion O22−".[1] --Itub (talk) 14:27, 3 September 2009 (UTC)
Okay, according to the definition in the Gold Book, that makes sense. Maybe it should be mentioned on the Perfluoroperoxide page that the name is misleading. RolfSander (talk) 16:00, 3 September 2009 (UTC)
The official name is Dioxygen difluoride which does indicate a fluoride. Yes, the alternate name perfluoroperoxide is misleading, but so are the alternate names of many other compounds.
As the best way to clear up this confusion, I am adding a note to this article to explain that OF2 and O2F2 are considered fluorides. Dirac66 (talk) 17:13, 3 September 2009 (UTC)

"Most" oxides?[edit]

The above discussion leads me to ask: why does the article say -2 in "most oxides"? If we exclude OF2 as an oxide, why not "all oxides" or just "oxides"? Are there exceptions which are clearly oxides? Dirac66 (talk) 17:25, 3 September 2009 (UTC)

I'd say there are no exceptions unless one used "oxide" in a loose sense in which peroxides, superoxides, etc. might be considered "kinds of oxides". --Itub (talk) 17:43, 3 September 2009 (UTC)
I think that peroxides, superoxides (and ozonides) definitely are oxides. Pyrite (FeS2) is definitely a sulfide of iron, after all. Why worry about it? There's an old joke: every general statement in inorganic chemistry has an exception, including this one! Otherwise, you end up saying that all oxides contain oxygen in the −2 oxidation state, and any binary compound of oxygen which doesn't have oxygen in the −2 oxidation state cannot be an oxide… rather circular as a description! Physchim62 (talk) 17:54, 3 September 2009 (UTC)
For CO it's -2 if the electrons are counted properly. There is a triple bond, but one is a dipolar bond which means that both electrons come from oxygen, so it does not change the oxidation state. See also Carbon monoxide#Resonance structure and oxidation state. Dirac66 (talk) 13:02, 15 March 2011 (UTC)

small contradiction between text and figure[edit]

In the image showing the acetaldehyde reaction (redox reacctions), the oxidation states of the two C atoms are shown with roman numerals. However, the clarification of the differences between "oxidation states" and "oxidation numbers" suggests that roman numerals are used for showing oxidation numbers, while arabic numerals are used for oxidation states. if anyone has the wherewithal to edit the svg file these perhaps ought to be swapped out with -3, +1, -3, and +3. — Preceding unsigned comment added by 68.238.86.7 (talk) 05:03, 6 July 2011 (UTC)

I think this image should be left unchanged. In structural diagrams for organic chemistry, oxidation states are often represented by Roman numerals to distinguish them from formal charges (calculated with all bonds covalent). The distinction between oxidation states and oxidation numbers is not important in organic chemistry. Dirac66 (talk) 16:28, 6 July 2011 (UTC)

Oxidisation of Polyethylene[edit]

Does anyone know whether this happens or not? 82.36.181.113 (talk) 22:34, 9 November 2011 (UTC)

Certainly if heated in the presence of oxygen. Polyethylene bags will burn in air if ignited with a match. Dirac66 (talk) 02:06, 10 November 2011 (UTC)
Answer 82.36.181.113 (talk) 05:40, 10 November 2011 (UTC)

Merge with oxidation number - as per other languages[edit]

May I suggest that the articles on Oxidation state and Oxidation number are so similar that they should be merged. One section of the merged article would be sufficient to explain the small difference between the terms in coordination chemistry.

My attention was drawn to the similarity on examining yesterday's edit of this article by Bgwhite, summarized as "Remove interwiki links as they point someplace else in Wikidata". In fact this editor removed 36 of the 41 interlanguage links, apparently because they pointed to articles in other languages which pointed back to Oxidation number and not here to Oxidation state. (At least this seems to be true for French, Spanish, German, Dutch and Russian, though not for Italian which was retained here.) In any case the Wikipedias in these languages all seem to have only one article, whether the title translates as Oxidation state or Oxidation number. So why do we need two articles in English for what is basically one concept? Dirac66 (talk) 01:04, 8 May 2013 (UTC)

Merge and redirect Both articles talk about both state and number. Both article have sections on what the difference is between number vs state. Both articles say, "The terms oxidation state and oxidation number are often used interchangeably." It would help the reader if information on both were in the same spot. Plus, it would make it easier to tell the difference between the two.
FYI... There are "only" 300,000 articles, categories and templates left with interwiki links. If you would like to help out, check out this page. Bgwhite (talk) 04:41, 8 May 2013 (UTC)
I would support a merge HOWEVER great care would be required. Oxidation number as based on the IUPAC definition is a taught concept at high school level that follows rules- this contrasts with the view of most practising chemists who typically use the old Pauling recommendations based simply on electronegativity difference. Lots of the pictures in this article are based on the Pauling model- which allows all atoms in a molecule to have their oxidation state determined whereas the IUPAC definition does not. I recently rewrote the oxidation number article because the difference between the o.s and o.n had been confused by the definitions in the IUPAC red book (which is out of date) which lead to the oxidation number article being contradictory. Axiosaurus (talk) 11:39, 15 May 2013 (UTC)
Yes, I agree that care will be required to properly relate the two (or several) related concepts and also to properly integrate the material in the two articles. I see that you have written about half of the current o.n. article, and that your rewrite involved thinking in detail about the concepts and also the sources, so that you are clearly very familiar with at least one of the two articles at the moment. So perhaps you would be the best person to go about actually performing the merger and producing a draft for the combined article. Since the proposal is only 8 days, however, we probably should wait another 2-3 weeks to determine consensus before making a decision to proceed. Dirac66 (talk) 20:22, 16 May 2013 (UTC)
It's been more than a month, and I support a merge, too. I'll also point out, in case the merge needs further justification, that the more subtly distinguished the topics, the more pedagogical benefit in describing them directly against each other. ENeville (talk) 22:23, 27 June 2013 (UTC)
Thanks for the support and the reminder. I have now started modifying this article and importing material from Oxidation number. When I have transferred all the non-redundant material here, I will replace Oxidation number by a redirect.
I have tried to point out the minor difference between oxidation number and oxidation state (as per Pauling), with one example where they are different because the metal is more electronegative than the ligand. As for IUPAC vs. Pauling, I think we need to show both ways since IUPAC is simpler and taught in high school, but the Pauling method can deal with nonequivalent atoms of the same element and so will always be used in practice for some molecules. Dirac66 (talk) 23:59, 30 June 2013 (UTC)
OK, the consensus was for merge with care. The merge is now complete, and I have tried to be careful. In some places I have changed "number" to "state" as per the context. Dirac66 (talk) 18:18, 1 July 2013 (UTC)

Halogen compound rule[edit]

This is a minor issue, but I stumbled over it. At Oxidation state § General rules for determining oxidation states without use of Lewis structures:

  • Halogens other than fluorine have an oxidation state of −1 except when they are bonded to oxygen, nitrogen, or another (more electronegative) halogen. For example, the oxidation state of chlorine in chlorine monofluoride (ClF) is +1. However, in bromine monochloride (BrCl), the oxidation state of Cl is −1.

It seems the parenthetical is actually a required part of the statement (i.e. not parenthetical) in order for it to be correct, right? That is, in all compounds of two halogens other than Fl, the more electronegative element has an OS of −1. —[AlanM1(talk)]— 22:50, 1 September 2013 (UTC)

I have replaced the parenthetical by a clause starting with which is, which expresses more clearly the intended meaning. Dirac66 (talk) 23:22, 1 September 2013 (UTC)

Merge[edit]

I feel a sense of deja vu, this is how it was before I rewrote the confusing and contradictory oxidation number article! Unnfortunately I was out of the country when this merge was agreed and made, and it had dropped off my watchlist.

This merged article has problems. Oxidation number is not given any prominence and yet that is what a lot of kids are taught not oxidation state. Some references are wrong, and it doesn't flow. Oxidation state as understood by older chemists and oxidation number as taught are different in detail and that has been obscured. I shall go back to the pre-merge version of oxidation number and try to put this merged version right. Axiosaurus (talk) 16:10, 10 September 2013 (UTC)

The pre-merge version of the oxidation state article was almost completely unreferenced, it also had some inaccuracies. I will make a start by flagging issues in the hope that some references may appear. Axiosaurus (talk) 03:22, 11 September 2013 (UTC)
The general rules section is contradictory. IUPAC states H is -1 with active metals and the article quotes boron (metalloid acording to some but never a metal!) as being an example where H has an oxidation state of -1. Applying the IUPAC definition would be a problem for most chemists as the concensus of most textbooks is that boron in BH3 has an oxidation state of +3. Applying the IUPAC rule B would obviosly have an oxidation state of -3 in borane. But BH3 reacts with Cl2 to form BCl3 and HCl and that is an oxidation. There is a paradox that in applying the IUPAC rules to BH4- the oxidation state of boron would be -5, which I agree appears odd. However the contradiction needs to be resolved.
The Lewis structures section is large and unreferenced. I find this section at best quaint. Is it actually taught or is this original work?

Axiosaurus (talk) 05:10, 11 September 2013 (UTC)

Using google I have found a possible reference to the lewis structures method in the text book - "Chemistry: Structure and Dynamics, James N. Spencer, George M. Bodner, Lyman H. Rickard, John Wiley & Sons, 28 Dec 2010", however the crucial parts of the book are not available- has anyone out there got access or another reference?Axiosaurus (talk) 08:55, 14 September 2013 (UTC)
References are hard to find for this topic. Many general chemistry books seem to give just the basic rules, while many inorganic and organic texts seem to assume that the reader already knows how to calculate oxidation states! Your reference to Spencer et al. may be useful though - Google gave me a relevant page with this URL:

http://books.google.ca/books?id=FRfcVwFr17IC&pg=PA543&lpg=PA543&dq=Spencer+Chemistry:+Structure+and+Dynamics+oxidation+state+Lewis+structure&source=bl&ots=PnvAGDKbVV&sig=CLcSZCFloSDI13wkvQggj6l5e64&hl=fr&sa=X&ei=R540UvrMG8XG4AO-2oGoAQ&ved=0CEcQ6AEwAw#v=onepage&q=Spencer%20Chemistry%3A%20Structure%20and%20Dynamics%20oxidation%20state%20Lewis%20structure&f=false Dirac66 (talk) 17:53, 14 September 2013 (UTC)

On rereading, this page of Spencer et al., it is much more detailed and explicit than the textbooks I had found, so I decided to include it as a source in the article. Thanks for suggesting the book. Dirac66 (talk) 00:35, 15 September 2013 (UTC)

Boron[edit]

The previous section notes a contradiction in the article concerning B-H bonds. Yes, of course the chemical consensus is that H is -1 when bonded to B. The only way I can understand the IUPAC list of exceptions is that it is not meant to be exhaustive. Exceptions ... are does not mean The only exceptions ... are. So yes, H is -1 when bonded to active metals (whatever that means exactly), but also when bonded to other metals as well as boron. Perhaps this point should be made in the article. Dirac66 (talk) 00:55, 15 September 2013 (UTC)

Hmm. Active metals is a fluffy term- by that I mean sometimes sometimes it just means reactive (as in reactivity series meaning), and I seem to remember a IUPAC paper which used the term with a list of relevant metals, and I will try to dig it out. You are right we need to draw attention to this apparent anomaly. The other issues I have with the IUPAC rules is that they need extension to cover oxygen fluorides and interhalogens, and the irony of that is a return to the classic electronegativity method. This point is well referenced - most basic text books add extra rules to cover these. So I think a list of problems with the IUPAC definition would be a good addition.Axiosaurus (talk) 09:59, 15 September 2013 (UTC)
Ideally we would like a magic recipe for oxidation state which can be concisely stated, has a logical basis and is completely general; but that does not really exist. The electronegativity (EN) method is concise and general, at least for molecules with localized 2c-2e bonds. However its logic is undermined by the arbitrariness of EN scales, which do not directly correspond to a measurable quantity and are not really meaningful for small EN differences. The current IUPAC definition reads as though a committee expressly set out to suppress the word electronegativity and replaced EN by a set of arbitrary rules with no justification given. These rules are far from general as we have agreed above, and IUPAC would need a much longer set of rules to be completely general. All Wikipedia can do here is maintain a neutral point-of-view (WP:NPOV) and outline the various approaches.
As for oxidation number vs. oxidation state, the only context in which I am familiar with a difference is in coordination chemistry if the metal is more electronegative than the ligand, as for the example given of Rh-P. Or did you mean that some authors use ON for Pauling and OS for IUPAC (or vice versa)?? Can you better express the difference between OS and ON, with examples if possible. Dirac66 (talk) 01:34, 18 September 2013 (UTC)
my understanding is that historically the terms have been used interchangeably. This seems to have changed when at some point in coordination chemistry, pre 2000, a different definition of ON (as per gold book) was introduced, further confused by the IUPAC 2005 inorganic naming conventions which used the term ON (this is not refelected in the gold book). I have made a start on a draft page of restructuring this article, I need to do a bit more before its worth reading. I will do my best to take your points on board re examples. At the mo. its 4:50 ish a.m. and this post is my cure for insomnia.Axiosaurus (talk) 03:55, 18 September 2013 (UTC)

"Formal" oxidation number[edit]

I removed the word "formal" whenever it appeared in "formal oxidation number". I hope this is okay. 178.38.121.208 (talk) 06:38, 23 October 2014 (UTC)

Anachronistic usage[edit]

Oxidation itself was first studied by Antoine Lavoisier, who believed that oxidation was always the result of reactions with oxygen,[16] thus the name. Although Lavoisier's idea has been shown to be incorrect, the name he proposed is still used, albeit more generally.

This seems to be using the term oxidation both circularly and anachronistically. If Lavoisier believed that oxidation always involved a reaction with oxygen, and this was a contentful statement rather than a tautology, then what did he mean by oxidation such that his belief could later be falsified? Whatever he meant by it should be described in this sentence by a word other than "oxidation", and the historical development will make more sense.

The following is closer to correct (and I have implemented it in the article). It's still anachronistic though, since Lavoisier could not have truly grasped what we now mean by oxidation. So what did he mean?

Oxidation itself was first studied by Antoine Lavoisier, who believed that what we now call oxidation was always the result of reactions with oxygen,[16] thus the name. Although Lavoisier's idea has been shown to be incorrect, the name he proposed is still used, albeit more generally.

178.38.121.208 (talk) 06:52, 23 October 2014 (UTC)

Another anachronism[edit]

A new second paragraph added today reads The term "oxidation" is derived from the element oxygen, which was the first atom known to pull electrons in a molecule toward itself, away from other atoms. Since Lavoisier is mentioned below, a historically naive reader might conclude that Lavoisier described oxidation in terms of electrons, which were in fact proposed over 100 years after his death.

A more historically accurate statement would be The term "oxidation" was first used by Lavoisier to mean reaction of an "oxidized" substance with oxygen. Much later, it was realized that the oxidized substance loses electrons, and the use of the term "oxidation" was extended to include other reactions in which electrons are lost. Dirac66 (talk) 16:46, 2 November 2014 (UTC)