Talk:Chemical substance

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Does chemicals include mining?

Should def 2 be moved to "chemical industry" or something like that? The idea with having this sort of an entry is to have a target to link to from descriptions of a nation's economy, such as Gabon/Economy.

"Chemical industry" sounds more English to me, FWIW. -- Marj Tiefert, Tuesday, April 23, 2002

There should be an article named chemical substance or substance (chemistry) for the meaning 1. Andres.

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[edit] Clarification of terms

The current definition of chemical substance is inadequate- it was originally written as a definition of the word "chemical" and is more appropriate for that.

We need two changes:

1. We need to revise the current definition for chemical substance.

2. We need definitions for BOTH the term chemical substance and the term chemical. The page for "chemical" (quite appropriately) gives a redirect to THIS page.

Regarding #1, I actually thought that an earlier definition of "chemical" (25 June 2004, see history) was a lot closer to the correct meaning of "chemical substance", but maybe others can supply an even better definition. The current definition (with its emphasis on process), with modification, might be an appropriate definition for the word "chemical", which in fact is what it was written for.

Regarding #2, I think we need to face up to the fact that "chemical" and "chemical substance" are NOT interchangeable terms. The ambiguity of meaning for the word "chemical" led this page to (thankfully!) be renamed as "chemical substance". Evidence for the difference in meaning:

  • In popular usage, the word "chemical" has a connotation of being artificial. Under this definition, chlorine is a chemical but chlorophyll is not. A Google search for "free from chemicals" gave 4750 hits, as opposed to only 45 hits for "free from chemical substances". Examples include baby products, organic food and aromatherapy oils. While some of us may chuckle at some of the claims made about such products, the fact remains that the word "chemical" is tainted by this.
  • In my copy of Encyclopædia Britannica (admittedly abridged to only 2CDs), the term "chemical" only ever seems to be applied to products of the chemical industry. The term chemical substance isn't in fact used in titles, though other terms such as chemical compound are used.

We can either give a common definition for both terms, followed by clarification of the vernacular usage of the term "chemical", or else we need two separate definitions. These same definitions might also be added to Category:Chemical_substances. Would someone care to write some definitions?

Walkerma 18:21, 31 Dec 2004 (UTC)

First, this is only a disambiguation page and there ought not be articles on "chemical" or "chemical substance", for they could only be dictionary entries, which is not what Wikipedia is about. This page is here only so that someone looking for "chemical" or "chemical substance" will find what they are looking for by following the links to which the page presently points.
The current definition is precisely the definition for "chemical substance".
Use in marketing is not a good way of seeing what a term means. The purpose of the industry is to attract consumers, without regard to strict discrete definitions. Ambiguity is encouraged so that consumers may equate or con-fuse two things which are in fact different. Anyhow, use in marketing is only a small part of the use of the word "chemical", which is more an abbreviation of "chemical substance" than an entirely different term. That a marketer prefers the simpler and shorter "chemical" to the longer "chemical substance" does not constitute a difference in meaning. In the Encyclopaedia Britannica (online edition), there is no entry for the word "chemical" or "chemical substance" because, as said above, such entries are not appropriate for an encyclopedia. The use of the word "chemical" in the EB is mostly as an adjective (relating to chemistry, etc.), because as a noun it is a nonspecific word that is inappropriate in an explicatory work.
There is nothing in a "chemical substance" (or "chemical"), in itself (per se), that distinguishes the substance from other things. Chemical elements and chemical compounds are only in the same category insofar as they are used in chemical processes, but they are not similar substances. What is a "chemical substance" if not a "chemical"? - Centrx 01:55, 2 Jan 2005 (UTC)

[edit] List of chemicals

Where would be a place for a list of chemicals like this: de:Chemikalienliste ? The thing closest to that seems to be Wikipedia:Chemical infoboxes which is surely not intended to be used as list of chemicals. 84.160.221.99 18:41, 23 Mar 2005 (UTC)

There is such a list, quite an extensive one, at List of compounds. In the English version we separate chemical elements from chemical compounds- so to get to the list like de:Chemikalienliste you need to follow the link to Chemical compound then you see it listed under "see also". I should mention that we are currently considering splitting list of compounds into organic and inorganic compounds, see Talk:List_of_compounds#propose_dividing_list_into_2_web_pages. I am still going through the organics, but I have done the inorganics, see List of inorganic compounds. Before this split started, I also started a page called Inorganic compounds by element, an alternative way of listing them, but I have suspended work on that until I finish doing List of organic compounds. Walkerma 23:01, 23 Mar 2005 (UTC)
Update- this split is almost complete- now a 3-way split- and list of compounds will cease to be a list at the end of May 2005. After this, please see list of biomolecules, list of organic compounds and list of inorganic compounds. Walkerma 17:19, 18 May 2005 (UTC)

[edit] Is this a disambiguation page?

I'm not sure this is really a disambiguation page. It's not so much that the term "chemical substance" is inherently ambiguous, merely that the term deliberately refers to a group of things, each of which has its own (comprehensive) article, and so an overarching article is unnecessary. It probably isn't necessary to disambiguate incoming links, because the term "chemical substance" is deliberately non-specific. So I'm proposing that the page be left as-is and merely the disambiguation notice be removed. Soo 00:57, 20 November 2005 (UTC)

I support that. Soo has summed up the situation eloquently - when people make a link to chemical/chemicals/Chemical substance (which all redirect here) they don't know if it's an ion/compund/element they just want a general discussion. Remove the {{disambig}} tag.--Commander Keane 19:46, 20 November 2005 (UTC)
Support. I agree, this page clearly is not a dab page, it is only structured as a dab page. It does need to be rewritten at some point and structured to be a regular article. Thaagenson 18:55, 28 November 2005 (UTC)
Done, {{disambig}} removed.--Commander Keane 18:43, 30 November 2005 (UTC)
I tentatively accept that this page may not be so strictly a disambiguation page, but what is the reason for the total reorganization of its content into several sections that clutter the page? - Centrx 19:38, 15 May 2006 (UTC)
Does Wikipedia cater only to professionals? Is there no room for an article that gives a reader a general idea of what a "chemical substance" might be without wading through 5 or 6 (or 10 or 12) other articles? Furthermore, based on the number of links to this article, some editors don't particularly care to distinguish what (if anything) they specifically mean by this term, either. Ewlyahoocom 10:58, 16 May 2006 (UTC)
You're absolutely right, it just needs someone to write it - and writing "general" articles like this is always harder than it seems (something like sodium hydroxide is much easier). Maybe this summer I'll have a go at writing this, though there are so many chem articles like this needing a lot of work. Maybe you could nominate it for the next Chemistry Collaboration of the Month? Walkerma 15:13, 16 May 2006 (UTC)
I do not object to this, per se, but this is not accomplished by simply copying the first paragraph of all of the other articles, and the way it was done sent the article off the screen where before it fit compactly. - Centrx 00:33, 18 May 2006 (UTC)

[edit] General overview?

Having noticed that you added the classification to it of "stub", I wonder what you think about how this article fits. It used to be classified as a disambiguation page that referred to the respective chemical element, chemical compound, atom, etc., but now it has been suggested to transform it into a top-level summary of a chemical substance in general. However, because of that, I don't see how it could ever become anything more than a stub. - Centrx 21:47, 24 May 2006 (UTC)

I agree that this page has never really been much more than a type of disambiguation page. It could be a full length article, though. At the chemistry wikiproject, it was listed on the worklist as one of the basic concepts in chemistry, and therefore worthy of an article, that's why it was picked out for assessment. I think at some point someone - maybe yours truly - will write a full article on the subject as it's pretty fundamental. Can you see a better way of covering the subject area? Walkerma 04:11, 25 May 2006 (UTC)

I can't think of what would be in it other than overviews of information already in other articles. General information about reactions? General safe handling? General information about chemistry, bonding..? - Centrx 06:28, 25 May 2006 (UTC)

Maybe you're right, I think we'll just have to see if someone gets around to writing it. Chemical compound is very short too, so there is "room" for coverage of this material. Walkerma 07:01, 25 May 2006 (UTC)

I changed the intro, and upgraded the rather nerdy description of the term 'chemical substance' to a more mondaine one .. isn't everything a chemical substance? What I mean is, the man in the street reads newspapers, and when a truck with ethanol has had an accident, the press describes the compound suddenly as a chemical substance. I think this page could be used to tell what a chemical substance is, I would even suggest to make some general compound point back to this page, if reasonably possible. No stub mark, not necessary, though it could use some more down-to-earth examples. But indeed, keep the page small and comprehensive. --Dirk Beetstra 07:50, 25 May 2006 (UTC)

Though all matter consists of chemical substances, any instance of matter is not an instance of a chemical substance. It is not accurate to say that "every substance is also a chemical substance". Mixtures are not chemical substances, it is not a chemical unit and it is not obtained by a chemical process; it is a physical process (in the large-scale Newtonian sense): you pour them together or such. The ethanol in the accident truck is a chemical substance, but the milk in such a truck is not. The air is not a chemical substance, and if the plastic in the casing of the reader's computer or the glass in the reader's water-drinking cup is a mixture, such as with coloring, then they are not chemical substances. - Centrx 23:42, 25 May 2006 (UTC)
Hmm, you are right, I agree. That sentence is not correct, and some others need some tweeking, I think the page is better of without that introductory section. But please help me getting the thing out that I try to tell, that many things are made of chemical substances, even if these compounds are NOT made by someone in a dirty white coat, with a pair of labglasses on his nose. So indeed, the milk in a similar truck is not a chemical substance, but a mixture of chemical substances, even if they are not man-made, most of them are made by (bio)chemical processes. And that was what the page was originally talking about, that all chemical substances were man-made. Thanks for the correction. --Dirk Beetstra 01:29, 26 May 2006 (UTC)
I think with mixtures, you only need make the phrase into the plural form "substances" and you're OK. I must say, the phrase "any material substance used in or obtained by a process in chemistry" really grates on me, it doesn't seem right. It implies that a chemical process is necessary to create it - not true. Furthermore, it carries nuances (not deliberately) that suggest that it has to come from a chemical plant, exactly the sort of thinking we want to avoid. I'm aware, though, that general terms such as this are the very hardest to pin down.
Getting to the earlier discussion, as I see it we could either have this article be extensive and leave chemical compound pretty short, or we could make this short and make chemical element and chemical compound longer, the main places where this sort of material is covered with. Which do you prefer? We can adjust the Chemistry WikiProject goals to match. I'm thinking of the high school student just learning about substances and compounds and mixtures, and who is trying to understand the concepts and associated aspects clearly. Walkerma 04:10, 26 May 2006 (UTC)

I do not agree with the intro now. Chemical substances are not only substances made by chemical industry or whatever, chemical substances are broader. I am reverting the edit. --Dirk Beetstra 13:43, 30 May 2006 (UTC)

The page said nothing about industry, and examples of air, rocks, and trees—let alone sugar, gold, and chairs—are not examples of things made in industry. Reverting the edit to a misleading revision without discussion is not the solution. You may object to constricting reference to chemistry in the first sentence, which I have changed so it is not confined to uses in chemistry. It does not accurate to excessively provide examples of general matter; "chemical substance" is not simply a synonym for "things" or "matter" or "stuff". — Centrx 02:19, 31 May 2006 (UTC)
No Centrx, it did, see [1]. That is what I reverted, substances are not chemical chemical substances when they are used in chemical industry. But we are reverting back and forth now, so that makes no sense. But I do believe that the examples can be better than what they are now, defining 'stone' as a mixture of chemical compounds does not clarify it enough in my opinion. The alcohol in a truck, used for chemical industry is nothing else than the alcohol they are drinking in a shot of whisky. --Dirk Beetstra 09:21, 31 May 2006 (UTC)
I think that the best solution to this is to look up some definitions in major reference works and textbooks, then cite the reference. I think we can find something that we can all agree on that way. I'm away at a conference, so I can't really do that now myself. Walkerma 13:56, 31 May 2006 (UTC)
Where does it refer to industry? If you mean chemistry, which is not confined to the "chemical industry", I have altered that sentence to possibly be more accurate. What is your specific objection? It can't be the business of an encyclopedia article to repeatedly re-assert identities, that yes, indeed, ethanol = ethanol. As for the truck and the whisky, the thing is that the whisky is something else than the ethanol in the truck, it has many other ingredients. -- Centrx 17:25, 31 May 2006 (UTC)
Oeps, you are right in that, I misread, sorry about that. But I think I disliked the 'process in chemistry', though it is true, it gives me a feeling of chemicals being only there in laboratories handled by (wo)men in white labcoats, or by large industries making a lot of black smoke, and not outside. But I think we agree now on the introductory sentence, no problems with that. It is closer to the point that I'd like to see in the article, everything is made up of chemical substances (either pure, or in mixtures). However, I do believe that expanding some examples as to what are the typical chemical substances in the normal things around the reader, both manmade, biochemical, as well as, due to fysical processes would help the explanation. --Dirk Beetstra 18:33, 31 May 2006 (UTC)

We seem to collide, but I see that you removed the 'back link' (which was difficult to give a proper position) to chemical substance on ion. I think that the definition on chemical substance should now be altered as well. I'll have a go. --Dirk Beetstra T C 08:45, 9 June 2006 (UTC)

You are right, it is a problem, but removing "ion" would entail the removal of "atom" and "molecule". An "atom" is not, a "molecule" is not, and an "ion" is not a chemical substance (in the way that "chemical substance", "chemical element", "chemical compound" are somewhat like mass nouns), but they are the fundamental units which together, respectively, make up a chemical substance. So, "atom" is under chemical element, "molecule" is under chemical compound (though, broadly all atoms are molecules, and there are some other ambiguities). What does "ion" go under though, possibly electrolyte, or possibly the current organization is not appropriate, or possibly they all should just be removed... -- Centrx 04:57, 11 June 2006 (UTC)
Martin Walker has told me that he has done a major offline rewrite of this article (see my talk page), I am waiting to see what he comes up with (which does not mean that we cannot edit this page, we might bring Martin Walker on additional ideas or subtilities. But in my feeling this is one of the top-level documents of 'chemicals', that is, it is a page that everybody reads, and I think there should be quite a short path 'up' here from commonly encountered chemicals (if people want to know about alcohol or sugar, they will see it is a chemical compound, and get technical data on ethanol (sugar), the first sentence there reads something like 'ethanol (sugar) is a chemical compound' .. then people might go up the tree, 'so, what is now really a chemical compound, I am drinking alcohol (coffee with sugar), what do I do, drink a chemical?', then there they will read what a chemical compound is, and then up to chemical substance (or 'substance (chemical)'), which, I think should then be written without any technicallities, telling that everything is made of (mixtures of) chemical compounds, giving very down to earth examples. But, as I said, I will wait for Martin's edit. --Dirk Beetstra T C 09:56, 11 June 2006 (UTC)

[edit] Explaining metal, bond, ion, etc.

Yes, all this information can be found by following the link (although in some cases the article introductions are not good for a layman). However, the purpose of transforming the article is to provide a high-level overview of chemical substances in general. Otherwise, there would be no reason to state how many known elements there are, or even that elements are divided into metals and non-metals in the first place, or that compounds are divided into organic and inorganic, or that some have covalent bonding and some ionic. All of this information is found in the linked articles, but if the purpose is a general overview, it needs to be consistent, even, and not skip explanations. —Centrx→talk 23:18, 13 June 2006 (UTC)

Yes, good point, I'll try and work on it if you don't get to it first. Regarding bonding, we need to keep things brief, because if we're not careful it could get off-subject. I tried to keep it focussed on things that have a "first-order" connection with chemical substances, but some "second-order" things like metals are close enough to first-order to warrant more detail in places. Thanks also to both Centrx and Dirk for the copyedits. Walkerma 04:59, 14 June 2006 (UTC)

Why do we study pure substances and mixtures?

To understand what everything (including ourselves) is made of, and how things interact with one another. Walkerma 03:42, 29 September 2006 (UTC)

[edit] Merge with chemical compound?

Should chemical compound and chemical substance be merged?--Smokefoot 13:26, 25 September 2006 (UTC)

No, don't think so. Sodium and certain alloys are chemical substances, but not chemical compounds.--Dirk Beetstra T C 14:00, 25 September 2006 (UTC)
I wish we could, because there is so much overlap, but unfortunately "substance" is broader because it includes chemical elements. If these were obscure terms it might be OK to merge and explain the differences on a single page, but in this case both pages probably get a lot of hits. Many high school students are unclear on these terms, so for the sake of clarity we should keep them separate. Walkerma 15:09, 25 September 2006 (UTC)

[edit] Rating

Upgraded it to Start. TerriG149.155.96.5 19:15, 27 October 2006 (UTC)

[edit] Definition

"A chemical substance is any material object that can undergo transformations responsible for a phenomena for example, a fire or an explosion." Other than the fact that phenomena is a plural (now fixed), can we have a citation for this description? A definition is the most critical part of an article, and this is one definition I have not seen. Please can you provide a reference for it. Thanks, Walkerma 16:51, 9 May 2007 (UTC)

I see that yoyu have reverted all my edits so far on this page just on the basis of the references from a text book or two. But, let me say that all text books are not always the best repositories of knowledge. They are often besotted with obsolete definitions. For example, can any body really assert that air, steel or brass is not a chemical substance. Limiting the definition of a chemical substance to pure substances: elements and compounds is plain simple narrow mindedness.Hallenrm 03:14, 10 May 2007 (UTC)
Actually, I didn't, I only did a minor copyedit, I was waiting for comments here before I did a full revert. We don't create new knowledge here, we only report what is commonly accepted (see Wikipedia:No original research) - and that means in the textbooks. If there is not a major body of opinion supporting the definition you provide, then it cannot be in Wikipedia. Can you provide some authoritative references for your assertion? Walkerma 03:20, 10 May 2007 (UTC)
A chemical substance is by definition pure. Certainly, any ordinary material substance is made up of chemical compounds, but that does not mean that any material substance is a chemical substance, and such a definition would be pointless, since matter is already a well-defined term with that meaning. You can find that definition in the dictionary, and you can find that definition in numerous academic and industry sources, in addition to the textbooks. You need to provide sources for your claim. See also Wikipedia:Verifiability and Wikipedia:No original research. —Centrx→talk • 03:27, 10 May 2007 (UTC)
Well if you want a reference to a text book here it is, It is a text book for class 7 students published by SCERT (the State Council of Educational Research and Training, Delhi) in 2004, it is entitled entitled "Do and Discover" These textbooks ate used by all the state supported schools in Delhi, (the total number of schools must be over 10,000) and by over a million students. Now, please don't say that a text book published in India has no weight in the academia.Hallenrm 03:32, 10 May 2007 (UTC)
Can you provide a reference that is available outside India that I can check? Unfortunately even WorldCat can't locate this book you mention. I tried looking at the Delhi Public Library site but they don't offer searches. It may be that in India this definition is used, whereas in the UK and the US the "pure substance" definition is used. We have Indian chemists on the chemistry WikiProject so I will check with them that this is mainstream opinion in India. Walkerma 04:07, 10 May 2007 (UTC)
I indeed expected that, that is the reason I carried out an extensive research on the Internet regarding the definition of chemical substance. While it is true that many sites use the definition of chemical substance that is almost similar to that of a chemical compound; the usage of the word on several sites (like the ones I have cited in the references) indicates a different meaning. The word chemical substance in a wikipedia article must reflect its current usage, rather than an archaic text book definition, that is my humble opinion, which is validated by the fact that alloys of uncertain composition find place in the chemical substance index compiled by the CAS (see ref 4 of the article)Hallenrm 06:47, 10 May 2007 (UTC)
Is a mixture of Fe and FeS2 one chemical substance or two chemical substances? If you say one, then how is a mixture defined? If you say two, then you are using the standard definition. The citations you've given are either unclear or they are obscure examples that simply reinforce the standard textbook definitions. That's why I'm reverting. The CAS chemical substance index obviously includes things of uncertain and variable composition, but these are generally defined as such. They are not going to publish a separate index called, "Chemical materials of uncertain and variable composition index" when it is clear they just mean mixtures of substances. Maybe the article should include a sentence or two about uncertain and variable compositions - that would be a very helpful addition to the article.
You also write, "some introductory textbooks" - can you find any mainstream textbooks with a different definition? You imply that the standard definition is "no longer current"; as someone who teaches chemistry full-time, this is news to me!
You seem to be confusing the words "material" which can include any collection of matter, with the term "substance" which means a particular type of matter. We have many schoolkids reading this particular article, and they need a simple, clear definition. They are likely to be confused by a definition that blurs things like this. Walkerma 16:01, 10 May 2007 (UTC)
Well, I notice that you have reverted all my edits, and in view of your lofty position in wikipedia I have no option but to accept your verdict. I can only say that you have not acted reasonably.Hallenrm 18:09, 10 May 2007 (UTC)
I want to see you convinced by rational argument! I have requested that others comment on this, to see if Centrx and myself are wrong. —The preceding unsigned comment was added by Walkerma (talk • contribs) 08:05, 11 May 2007 (UTC).
I am sorry, but the version as it stands now has a reference to a reasonably new book. I would not call that an 'archaic' definition.
I think the aim of this document is to give a generally accesible definition, and, maybe, it should later in the document define that definition more precisely. Our aim in our major rewrite has been that the definition of a chemical substance was so that it would not sound like 'chemical substances are scary', no, everything around you is made up of chemical substances, and water being a good example. Also, helium is a chemical subtance, hardly any real-life phenomena are related to that (except for its low density as a gas which has a function in balloons or to alter voice). That is quite contrary to the definition 'A chemical substance is any material object that can undergo transformations responsible for a phenomena for example, a fire or an explosion.' (helium being unreactive and most phenomena of it are physical). That stigmatises chemistry again as something that is dangerous, which it is not.
I think our approaches to this document have been different, where we tried to give a simple, generally correct definition, you want to start the document with a definition that is complete and correct. Though both approaches are possible, we have discussed the point, and put the more difficult cases and exceptions in later parts of the document (but we may have overseen some).
So for now I would suggest to leave the introduction as is (it is backed up with a reasonably new, generally accessible reference, and I think that more general chemistry books could do the same function), but you are more than welcome to further sharpen the definition in a later paragraph. And indeed alloys are there a good point, and they should be mentioned, they can be seen as mixtures of chemical compounds, but they also do have chemical properties that are specific to the alloy. Hope this helps, have a nice day. --Dirk Beetstra T C 10:46, 11 May 2007 (UTC)

[edit] What is a chemical substance?

The current introductory lines of the article define a chemical substance as "any material with a definite chemical composition.[1] For example, a sample of water has the same properties and the same ratio of hydrogen to oxygen whether the sample is isolated from a river or made in a laboratory."which is neither the uniequivocal usage of the term neither very precise. For example, the Chemical substances Index published by CAS includes many substances like alloys of variable composition. Is CAS mistaken in including these substances in a list of chemical substances? CAS is an undisputed body of chemistry professionals, to say that their decisions are not in consonance with the accepted common knowledge of chemists and cite a statement on the basis of a text book would definetly not in the line of the wikipedia objectives. Secondly, the article has the phrase mechanical process; what really are mechanical processes, and are they always useful to separate the component of a mixture?Is the readership of wikipedia limited to school kids? Even if it is, wouldn't it be better to present a balanced opinion rather than harping on the traditional statement. The objective of Wikipedia, in my opinion is to reflect the changing nature of knowledge based on inputs from general public rather than repeating the oft quoted definitions for which Encyclopedia Britannica, Encyclopedia Americanna or for that mattewr MSN encyclopedia are much better known for. These are a few questions I would like to raise, simply because I am a firm believer of the spiritof Wikipedia and I do not belong to the conservative classHallenrm 07:37, 11 May 2007 (UTC)

Unfortunately Wikipedia has to be conservative, since WP:NOR requires it. Wikipedia merely attempts to report the mainstream body of opinion on a topic. Although the body of an article can mention controversies or alternative viewpoints, the introductory section has to reflect the consensus view on the topic, which in this case means the mainstream view of the chemical community. Regarding CAS, I replied on that topic above, and I agree that the body of the article could include some discussion of the fuzziness of the "pure substance" concept in certain cases. Walkerma 08:05, 11 May 2007 (UTC)
"The objective of Wikipedia, in my opinion is to reflect the changing nature of knowledge based on inputs from general public rather than repeating the oft quoted definitions". Then you don't agree with the core Wikipedia policies such as Verifiability and No Original Research. This is going to be a problem. --Itub 08:07, 11 May 2007 (UTC)


Getting back to the topic, I think there's some truth to both sides. The definition of "substance" is a bit blurry, which is why sometimes "pure substance" is used for emphasis. There are some gray areas: I would say that non-stoichiometric compounds are generally considered substances, despite their continuously variable range of compositions (I think they should be mentioned and linked somewhere in the article). But I wouldn't go to the extreme of saying "any material object that can undergo transformations"; I wouldn't say gunpowder is a chemical substance, but a mixture. Another concept that is more precisely defined and that should be linked from the article is chemical species. --Itub 08:24, 11 May 2007 (UTC)

While I can understand why Hallenrm might wish to expand the definition of "chemical substance", the one that is proposed is simply not up to the job. It confuses "material object" with "matter", for a start... The IUPAC definition is:
Matter of constant composition best characterized by the entities (molecules, formula units, atoms) it is composed of. Physical properties such as density, refractive index, electric conductivity, melting point etc. characterize the chemical substance.
The requirement for constant composition is usually taken to exclude mixtures, defined as "Portion[s] of matter consisting of two or more chemical substances called constituents", although things get more complicated when you start talking about nonstoichiometric compounds such as iron(II) oxide. Chemical species and molecular entity are more precisely defined terms if needed (note that there is a seperate definition for the chemical species of an element in toxicology).
On a practical level, a chemical substance incluses both chemical elements and chemical compounds: in both cases, their composition is unaffected by a physical change. The composition of a mixture is affected by a physical change, see distillation. The distinction is not merely useful, but central to chemistry and should not be played about with in this way. Physchim62 (talk) 12:37, 11 May 2007 (UTC)


I find the definition "any material object that can undergo transformations responsible for a phenomenon such as a fire or an explosion can be called a chemical substance" completely unacceptable as it is written. It could be interpreted in a way that is far too broad - under this definition what would distinguish any material object from a chemical substance? For example, my house could be considered a chemical substance because it is a material object that can be burned in a fire. The definition "a chemical substance is any material with a definite chemical composition" is more precise, conistent with historical meaning, consistent with modern use, and broadly used in the chemical community (both industry and academics). It is clearly the more appropriate definition for this article. --Ed (Edgar181) 12:56, 11 May 2007 (UTC)

Although there are a growing number of examples of materials that struggle to fit into the traditional definitions and are on the fuzzy borders I do not see a need (I'm talking broadly not WP) to abandon all classifications as is being suggested. Obviously I do not agree with the proposed definition for use here given that this is the last place any change in consensus should be proposed. These examples of poorly defined chemical substances should be mentioned as they are important to the relevance of the concept. I.e. some things don't fit well. Superconducting ceramics with irrational fractional compositions are a great example where the distinction between a chemical substance and a mixture becomes blurry. There are many other examples for other scientific definitions too. These are generally very scientifically interesting. The fact that nature gives us gray areas doesn't mean that we should abandon all organizing principles. It simply means that we should recognize that reductionism has its limits. --Nick Y. 17:08, 11

May 2007 (UTC)

IMHO, there should be minimal overlap between different terms used in science, in this case there is apparently a lot of overlap in the usage of the terms like matter, chemical compound; chemical species, chemical substances, pure substance and chemical element which can lead to a lot of confusion in the mind of a school student who is learning the terms. Their is a need to reduce this confusion and all attempts must be made to do so. In the present case, the present definition can be reduced to A chemical substance can either be an element or a compound , which does not leave the room for any doubt regarding different isomers of a compound or isotopes of an element. How about this much more viable practical definition "a chemical substance is a substance listed in the chemical substance index with a link to the index and the numbers. It leaves very little room for any ambiguity and is distincly different from the definition for a compound or pure substance. There is a need for wider discussion and consensus on this matter, I believe a UK university indeed conducted a seminar on this topicHallenrm 02:55, 12 May 2007 (UTC)
Defining a chemical substance as "anything that appears in the CAS index" is nonsensical. It would be replacing a scientific definition by a completely arbitrary one based on what a particular organization decides to put in its index, and does not answer "how do they choose what to put on the index?". In any case, the CAS definition is a pragmatic one based on what CAS users may want to search and not on a scientific definition of "substance". If there is overlap between terms in science, it is not our position to get rid of the overlap by inventing new definitions; that would be just opinion and original research which have no place on Wikipedia. --Itub 07:38, 12 May 2007 (UTC)
I think that the latest addition to the introduction by Hallenrm is a good one (though I have moved it a bit around). I don't know too much about alloys, but can alloys be separated by physical means (e.g. zone melting or centrifugal force?), if there are examples maybe that should be added to that sentence. I also think that a paragraph should be added (lower in the document, I would say after 'chemical compounds') where the more borderline cases are explained (alloys, e.g.). The intro should then point to that paragraph.
I second Itub with that a chemical substance is not a chemical substance because CAS or whatever organisation has given it a CAS-number (or the like). Hope this helps. --Dirk Beetstra T C 07:52, 12 May 2007 (UTC)
It's a much better intro, now, and I think the mention of the alloys is reasonable now. I agree with Itub and Dirk regarding CAS definitions. Thanks to all! Walkerma 17:48, 14 May 2007 (UTC)

Just one more point regarding CAS. After looking at the reference provided, I noticed that the CAS index also lists elementary particles such as quarks, muons, etc. I hope no one will argue that they are "chemical substances"! --Itub 17:45, 15 May 2007 (UTC)

Atkins and Jones "Chemistry: Molecules, Matter and Change", 3rd Ed has this to say on page 1, "Each different pure kind of matter is called a substance. By pure, we mean the same throughout, even on a microscopic scale. Thus, iron is one substance; water is another. Notice that the scientific meaning of the term substance is a little different from its everyday meaning. A substance in science is a single, pure form of matter, not a mixture of several kinds of matter." That has always been my understanding. --Bduke 08:31, 16 May 2007 (UTC)

[edit] isomerism and tautomerism

I have problems with this recent edit:-

"A particular composition of a particular set of elements can be present in the form of several chemical organic compounds; this is so because of isomerism and tautomerism."

There is a clear difference, in the context of chemical substances. If several isomers are present, there are several chemical substances. Tautomerism is when two isomers, of a kind, are in chemical equilibrium. Mostly a mix of isomers is not, by a long way, in equilibrium. Dimethyl ether and ethanol are isomers, but they are not in equilibrium. One is more stable, but either can exist, essentially for ever, as the barrier for interconversion is so high. Yes, it is a gradation, but like the difference between strong and weak acids there is a clear difference between isomers not in equilibrium and those that are. We call the latter tautomers. If they are in equilibrium we call it one chemical substance. If they are not in equilibrium we say they are different chemical substances. In the case of weak acids we say acetic acid is one chemical substance even though there are three species - acid, H cation and anion. In the case of strong acids we sometimes say there are two chemical substances - cation and anion - but I agree that sometimes we say there is just one substance. It depends on the context there. Nevertheless isomers and tautomers are quite different. --Bduke 12:38, 19 May 2007 (UTC)

I would like to add, isomers that are in equilibrium in a solution in a solvent cannot be called a single substance; so only if glacial acetic acid is cent percent pure it can be called a pure substance. I am not very sure if in absolutely pure acid there are independent hydrogen ionsHallenrm 02:33, 20 May 2007 (UTC)
I think I disagree. Acetic acid in water is two chemical substances even though the acetic acid is in equilibrium with hydronium and acetate ions. Similarly if a ketone is mixed with water and there are keto and enol forms, we still say there are two chemical substances, ketone and water, not three. However if n-propyl alcohol and tert-propyl alcohol are mixed there are two substances because these two isomers are not in equilibrium due to the very low kinetic rate of interconversion between the isomers. It is a pragmatic decision based largely on what we get after simple physical separation methods such as distillation. --Bduke 05:35, 20 May 2007 (UTC)
One definition of tautomerism (not quite the official one) is that two tautomers cannot be seperated by physical or chemical means, whereas two "normal" isomers can be. Most people would consider acetone to be a single chemical substance, even if it is a mixture of two molecular species. Physchim62 (talk) 09:14, 21 May 2007 (UTC)

Same can be said for acetic acid. Even the most pure acetic acid will contain acetate and protonated acetic acid ("acetonium"?) ions, same as water contains hydronium and hydroxide ions. Perhaps there is also some acetic anhydride and water in equilibrium with your acetic acid. And there are the acetic acid dimers, which, depending on the context, might be counted as different species. I agree with Physchim62's definition, but as usual, there are gray areas. The difference between isomer, tautomer, and even conformer depends on temperature. --Itub 09:26, 21 May 2007 (UTC)

Pure substance dah  —Preceding unsigned comment added by 99.226.96.83 (talk) 22:52, 25 November 2007 (UTC)