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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.
It's quite strange that on the Chemistry page it's says that "water" are a Compound. and on this page it is stated that "water" are a substance. now I just started learning Chemistry and I find this strange and inconsistent. 84.229.175.145 ( talk) 21:42, 16 July 2011 (UTC)Elad
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:
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)
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)
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)
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 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)
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)
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)
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)
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?
Should chemical compound and chemical substance be merged?-- Smokefoot 13:26, 25 September 2006 (UTC)
Upgraded it to Start. TerriG 149.155.96.5 19:15, 27 October 2006 (UTC)
"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)
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 class Hallenrm 07:37, 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)
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)
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)
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)
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)
I just created the entry for Reagent bottle. If you have more useful and knowledgeable information, please do add it. Radical Mallard ( talk) 16:53, 6 July 2010 (UTC)
The definition is given like this: "In chemistry, a chemical substance is a material with a specific chemical composition." "Chemical composition" links to Chemical compound, while chemical compound is said there to consist of two or more different chemical elements. (Say, oxygen consists of one.) Thus, the link is irrelevant. Jack who built the house ( talk) 10:45, 30 November 2010 (UTC)
My suggestion is to link Chemical formula, though it itself is defined as "a way of expressing information about the atoms that constitute a particular chemical compound", again. But I think this is not a matter of principle there. Jack who built the house ( talk) 11:40, 30 November 2010 (UTC)
I suggest to change the main definition to "A chemical substance is a form of matter that has constant composition and characteristic properties. It can not be separated into components by physical separation methods, i.e. without breaking chemical bonds. Often, chemical substances are called pure substances to set them apart from mixtures".
The current definition reads "A chemical substance is a material with a specific chemical composition", with a citation to the IUPAC gold book. However, it is not carefully cited. The gold book has a longer definition that continues "Physical properties such as density, refractive index, electric conductivity, melting point etc. characterize the chemical substance". Leaving out this part distorts the meaning. According to the short definition, dioxygen and ozone would be the same substance (and all sets of allotropes), as would be ethanol and dimethyl ether (and all sets of isomers). It is difficult to find a definition that deals correctly with all borderline cases without getting overly long, but the current definition is too short to be accurate.
A good definition has to incorporate our understanding of a pure substance both at the macroscopic and the atomic level.
On the macroscopic level, a chemical substance has a constant composition (not specific composition, this would include a one molar sodium chloride solution, which is a mixture) and characteristic properties. It can not be separated into different components by physical methods such as evaporation, distillation, chromatography, zone melting or dialysis. A sodium chloride solution would not be classified as a chemical substance because it can be separated into pure sodium chloride and pure water, and because its physical properties such as density depend on the concentration of the solution.
On the atomic level, a chemical substance contains a set of atoms that have characteristic bonds to other atoms. No matter if a substance is a noble gas, a molecular compound, a solid ionic compound, a network solid, a metal or something more exotic, it is always possible to make a short list of atoms and describe how they are bonded to the other atoms in the list. The stoichiometry of the atoms in this list is constant, and the chemical formula of the substance summarizes that list. Every atom in the chemical substance is described by the list.
This is what the definition has to capture. Complications, such that water in the liquid phase partially dissociates, distract from the main idea, and should be dealt with further into the article. Similarly, the question of rapidly interconverting isomers, polymers with a range of chain length, isotopic composition etc. should be dealt with outside the lede. -- Theislikerice ( talk) 04:04, 11 February 2011 (UTC)
If you go to chemical compound it says much the same thing. The problem is that this is true only part of the time (i.e. for only some types of compounds). Yes, some chemical substances and chemical compounds have fixed ratios of atoms held together by chemical bonds (constant composition), but others do not-- and yet are clearly NOT mixtures. Atoms in a sample of matter may all be held together by ionic or covalent bonds, but they often, in fact usually do not have neat empirical formulas that you could write down on a bottle label. Most of the mantle and crust of our planet is such stuff--for example, all those plagioclase feldspars that don't have clearly defined stoichiometry. These articles are confused, as though minerology was all like biochemistry. We need to make it clear that whole-number stoichiometry sometimes happens, but usually it is just an ideal. Fixed ratios of atoms are the exception in nature, not the rule. These nice formulas are only a small subset of chemical substances and compounds in the "real" world. S B H arris 06:43, 26 February 2012 (UTC)
I have revised the Definition section, and will allow this to settle a bit. The lede and the definition section are not yet consistent, nor is the whole of this article consistent with the whole of Chemical compound. Compare the lede at Chemical compound with the Definitions section here. See also the comments made in response to Mr Harris at the chemical compound page. Le Prof 71.201.62.200 ( talk) 21:49, 2 July 2015 (UTC)
Note, it is Wikipedia policy that it is sufficient to make statements in the lede that are substantiated, in the main body, through verifiable citations. It is for this reason that the lede does not bear any citations. The supporting citations for the lede appear in the main body of the article. Please, edit away, if you are a well trained chemist, or a chemical educator. If you do not understand the field, please discuss first. Cheers, Le Prof 71.201.62.200 ( talk) 00:45, 24 August 2015 (UTC)
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Currently the definition is ( version used at the moment of this comment):
1. First the IUPAC definition is not completely cited. This is important because when I read the complete definition of IUPAC, I have
And when I look at the words of the definition, I can see that the plural form is used for molecules. Then there is no exclusion when citing the different entities of a substance. We can admit that a substance can be composed of one type of molecules like water as solvant with some ions like NaCl dissolved in it. So nothing in the IUPAC definition prevents to include mixture under the term of chemical substance. But several constraints limits the use of chemical substance to only defined mixture. Aqueous solution of NaCl can't be considered as chemical substance because it doesn't respect the defined composition and the defined physical properties. But solution of NaCl 1M can be considered as a chemicla substance because the composiiton is defined and physical properties can be measured and compared.
2. Nothing in the IUPAC definition mention the characteristic of "it cannot be separated into components by physical separation methods, i.e., without breaking chemical bonds". In order to assess the validity of this additional definition, a reference has to be provided: it is not correct to create a definition from different sources without providing the sources. If there are different sources with different characteristics, this should be described in the definition section of the article and not merged into one WP definition in the introduction.
3. Then when citing the different classes which can considered as chemical substance, the alloys don't really fit with the "it cannot be separated into components by physical separation methods": some alloys can be partially melted in order to create a liquid phase rich in one metal and a solid phase poor with the same metal (see this diagram fo the copper-silver alloys). So if we agree that we can modify the composition of some alloys by melting and/or crystallization (I am not familiar with metal chemitry), then we can't keep the "it cannot be separated into components by physical separation methods" as characteristics of the chemical substance (or we should remove alloys as part of chemical substance).
4. The list of subclasses for chemical classes is in contradiction with the IUPAC définition: ions and chemical elements can't be considered as chemical substance as we can't measure the density or the melting point of ions or chemical elements. In case of ions because we an't isolate pure ion forms, same for chemical elements (we don't measure the density of hydrogen atom but the one of dihydrogen molecule). So the list sould be chemical compounds, alloys, simple substances (like dihydrogen, dioxygen,...) and mixtures which have a defined composition.
In my opinion we should rely only on the IUPAC definition in the introduction: IUPAC is the reference in chemical nomenclature so we should always considered this definition as the first one. Other definitions should be cited in the definition section with some elements about the application of the definition. For example, I don't think that ECHA definitions for chemical substance has any influence in Asia (if we exclude the commercial exchanges between Asia and Europe), so indicating ECHA definitions is kind of western or at least european oriented defition and cannot be considered with the same authority as for IUPAC. Same for textbooks. Snipre ( talk) 03:21, 10 June 2017 (UTC)
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Hi, this is my first time trying to edit Wikipedia, and I thought that since this is a "vital article" that I should first propose the change on the talk page. I've just started to learn biology and I've been struggling a bit with all of the various definitions. My understanding is that a molecule is when two elements covalently bond, but it's only a compound if the elements are different. However, the last sentence in the first paragraph doesn't include this case (for example, H2), i.e. it doesn't include molecules in its list of examples which would cover this case. The IUPAC Gold Book's definition of chemical substance does include molecules. Therefore, for clarity and completeness, I propose adding molecules to the list of examples in the last sentence of the first paragraph. -- Freeradical137 ( talk) 06:53, 8 April 2018 (UTC)
Substance and body are disjunctive concepts. Since the terms are interrelated, I recommend the following supplement:
Even
Aristotle distinguished between substance (substance) and form (body): the substance is the formless, rigid substance, the "underlying", the form (body) its shape. Wood and Marble eg are fabrics, the finished plate or sculpture the shape. The sand castle disintegrates the sand remains. Fabric and form are sides of a concrete individual thing and do not occur independently:
more material term | wood | wood | water | diamond | paper | air | –– | rain | glass | iron |
---|---|---|---|---|---|---|---|---|---|---|
more physical term | plate | dowel | beam | crystal | sheet | balloon | electron | areal | glass | atom |
Remarks:
Walmei ( talk) 11:34, 1 July 2018 (UTC)
Why element sometimes called pure 2A02:C7F:C297:9A00:ED0E:40FF:76DC:376D ( talk) 17:54, 27 February 2022 (UTC)
What is pure
substances 2409:4056:191:575B:0:0:2710:A0B1 ( talk) 00:34, 14 May 2022 (UTC)
I have just published some significant edits to the introduction, tagging along with my reasoning here. Broadly, my goals were to improve the readability and understanding here. These included corrections to some inaccurate/misleading information.
Feel free to edit as desired, or commence discussion here. AdmiresCycles ( talk) 06:57, 7 January 2024 (UTC)
Chemicals are products of industry, have a purpose and declared purity. The name is not an abbreviation of chemical substances nor its synonym.
Chemical substances are hierarchically above chemicals. All chemicals are chemical substances, but only some chemical substances are chemicals.
Whoever merged these two articles is clueless and is stomping on established scientific nomenclature just because some people don't understand the difference and say "all chemicals are bad". Lajoswinkler ( talk) 19:40, 22 January 2024 (UTC)
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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.
It's quite strange that on the Chemistry page it's says that "water" are a Compound. and on this page it is stated that "water" are a substance. now I just started learning Chemistry and I find this strange and inconsistent. 84.229.175.145 ( talk) 21:42, 16 July 2011 (UTC)Elad
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:
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)
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)
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)
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 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)
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)
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)
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)
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?
Should chemical compound and chemical substance be merged?-- Smokefoot 13:26, 25 September 2006 (UTC)
Upgraded it to Start. TerriG 149.155.96.5 19:15, 27 October 2006 (UTC)
"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)
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 class Hallenrm 07:37, 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)
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)
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)
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)
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)
I just created the entry for Reagent bottle. If you have more useful and knowledgeable information, please do add it. Radical Mallard ( talk) 16:53, 6 July 2010 (UTC)
The definition is given like this: "In chemistry, a chemical substance is a material with a specific chemical composition." "Chemical composition" links to Chemical compound, while chemical compound is said there to consist of two or more different chemical elements. (Say, oxygen consists of one.) Thus, the link is irrelevant. Jack who built the house ( talk) 10:45, 30 November 2010 (UTC)
My suggestion is to link Chemical formula, though it itself is defined as "a way of expressing information about the atoms that constitute a particular chemical compound", again. But I think this is not a matter of principle there. Jack who built the house ( talk) 11:40, 30 November 2010 (UTC)
I suggest to change the main definition to "A chemical substance is a form of matter that has constant composition and characteristic properties. It can not be separated into components by physical separation methods, i.e. without breaking chemical bonds. Often, chemical substances are called pure substances to set them apart from mixtures".
The current definition reads "A chemical substance is a material with a specific chemical composition", with a citation to the IUPAC gold book. However, it is not carefully cited. The gold book has a longer definition that continues "Physical properties such as density, refractive index, electric conductivity, melting point etc. characterize the chemical substance". Leaving out this part distorts the meaning. According to the short definition, dioxygen and ozone would be the same substance (and all sets of allotropes), as would be ethanol and dimethyl ether (and all sets of isomers). It is difficult to find a definition that deals correctly with all borderline cases without getting overly long, but the current definition is too short to be accurate.
A good definition has to incorporate our understanding of a pure substance both at the macroscopic and the atomic level.
On the macroscopic level, a chemical substance has a constant composition (not specific composition, this would include a one molar sodium chloride solution, which is a mixture) and characteristic properties. It can not be separated into different components by physical methods such as evaporation, distillation, chromatography, zone melting or dialysis. A sodium chloride solution would not be classified as a chemical substance because it can be separated into pure sodium chloride and pure water, and because its physical properties such as density depend on the concentration of the solution.
On the atomic level, a chemical substance contains a set of atoms that have characteristic bonds to other atoms. No matter if a substance is a noble gas, a molecular compound, a solid ionic compound, a network solid, a metal or something more exotic, it is always possible to make a short list of atoms and describe how they are bonded to the other atoms in the list. The stoichiometry of the atoms in this list is constant, and the chemical formula of the substance summarizes that list. Every atom in the chemical substance is described by the list.
This is what the definition has to capture. Complications, such that water in the liquid phase partially dissociates, distract from the main idea, and should be dealt with further into the article. Similarly, the question of rapidly interconverting isomers, polymers with a range of chain length, isotopic composition etc. should be dealt with outside the lede. -- Theislikerice ( talk) 04:04, 11 February 2011 (UTC)
If you go to chemical compound it says much the same thing. The problem is that this is true only part of the time (i.e. for only some types of compounds). Yes, some chemical substances and chemical compounds have fixed ratios of atoms held together by chemical bonds (constant composition), but others do not-- and yet are clearly NOT mixtures. Atoms in a sample of matter may all be held together by ionic or covalent bonds, but they often, in fact usually do not have neat empirical formulas that you could write down on a bottle label. Most of the mantle and crust of our planet is such stuff--for example, all those plagioclase feldspars that don't have clearly defined stoichiometry. These articles are confused, as though minerology was all like biochemistry. We need to make it clear that whole-number stoichiometry sometimes happens, but usually it is just an ideal. Fixed ratios of atoms are the exception in nature, not the rule. These nice formulas are only a small subset of chemical substances and compounds in the "real" world. S B H arris 06:43, 26 February 2012 (UTC)
I have revised the Definition section, and will allow this to settle a bit. The lede and the definition section are not yet consistent, nor is the whole of this article consistent with the whole of Chemical compound. Compare the lede at Chemical compound with the Definitions section here. See also the comments made in response to Mr Harris at the chemical compound page. Le Prof 71.201.62.200 ( talk) 21:49, 2 July 2015 (UTC)
Note, it is Wikipedia policy that it is sufficient to make statements in the lede that are substantiated, in the main body, through verifiable citations. It is for this reason that the lede does not bear any citations. The supporting citations for the lede appear in the main body of the article. Please, edit away, if you are a well trained chemist, or a chemical educator. If you do not understand the field, please discuss first. Cheers, Le Prof 71.201.62.200 ( talk) 00:45, 24 August 2015 (UTC)
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Currently the definition is ( version used at the moment of this comment):
1. First the IUPAC definition is not completely cited. This is important because when I read the complete definition of IUPAC, I have
And when I look at the words of the definition, I can see that the plural form is used for molecules. Then there is no exclusion when citing the different entities of a substance. We can admit that a substance can be composed of one type of molecules like water as solvant with some ions like NaCl dissolved in it. So nothing in the IUPAC definition prevents to include mixture under the term of chemical substance. But several constraints limits the use of chemical substance to only defined mixture. Aqueous solution of NaCl can't be considered as chemical substance because it doesn't respect the defined composition and the defined physical properties. But solution of NaCl 1M can be considered as a chemicla substance because the composiiton is defined and physical properties can be measured and compared.
2. Nothing in the IUPAC definition mention the characteristic of "it cannot be separated into components by physical separation methods, i.e., without breaking chemical bonds". In order to assess the validity of this additional definition, a reference has to be provided: it is not correct to create a definition from different sources without providing the sources. If there are different sources with different characteristics, this should be described in the definition section of the article and not merged into one WP definition in the introduction.
3. Then when citing the different classes which can considered as chemical substance, the alloys don't really fit with the "it cannot be separated into components by physical separation methods": some alloys can be partially melted in order to create a liquid phase rich in one metal and a solid phase poor with the same metal (see this diagram fo the copper-silver alloys). So if we agree that we can modify the composition of some alloys by melting and/or crystallization (I am not familiar with metal chemitry), then we can't keep the "it cannot be separated into components by physical separation methods" as characteristics of the chemical substance (or we should remove alloys as part of chemical substance).
4. The list of subclasses for chemical classes is in contradiction with the IUPAC définition: ions and chemical elements can't be considered as chemical substance as we can't measure the density or the melting point of ions or chemical elements. In case of ions because we an't isolate pure ion forms, same for chemical elements (we don't measure the density of hydrogen atom but the one of dihydrogen molecule). So the list sould be chemical compounds, alloys, simple substances (like dihydrogen, dioxygen,...) and mixtures which have a defined composition.
In my opinion we should rely only on the IUPAC definition in the introduction: IUPAC is the reference in chemical nomenclature so we should always considered this definition as the first one. Other definitions should be cited in the definition section with some elements about the application of the definition. For example, I don't think that ECHA definitions for chemical substance has any influence in Asia (if we exclude the commercial exchanges between Asia and Europe), so indicating ECHA definitions is kind of western or at least european oriented defition and cannot be considered with the same authority as for IUPAC. Same for textbooks. Snipre ( talk) 03:21, 10 June 2017 (UTC)
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Hi, this is my first time trying to edit Wikipedia, and I thought that since this is a "vital article" that I should first propose the change on the talk page. I've just started to learn biology and I've been struggling a bit with all of the various definitions. My understanding is that a molecule is when two elements covalently bond, but it's only a compound if the elements are different. However, the last sentence in the first paragraph doesn't include this case (for example, H2), i.e. it doesn't include molecules in its list of examples which would cover this case. The IUPAC Gold Book's definition of chemical substance does include molecules. Therefore, for clarity and completeness, I propose adding molecules to the list of examples in the last sentence of the first paragraph. -- Freeradical137 ( talk) 06:53, 8 April 2018 (UTC)
Substance and body are disjunctive concepts. Since the terms are interrelated, I recommend the following supplement:
Even
Aristotle distinguished between substance (substance) and form (body): the substance is the formless, rigid substance, the "underlying", the form (body) its shape. Wood and Marble eg are fabrics, the finished plate or sculpture the shape. The sand castle disintegrates the sand remains. Fabric and form are sides of a concrete individual thing and do not occur independently:
more material term | wood | wood | water | diamond | paper | air | –– | rain | glass | iron |
---|---|---|---|---|---|---|---|---|---|---|
more physical term | plate | dowel | beam | crystal | sheet | balloon | electron | areal | glass | atom |
Remarks:
Walmei ( talk) 11:34, 1 July 2018 (UTC)
Why element sometimes called pure 2A02:C7F:C297:9A00:ED0E:40FF:76DC:376D ( talk) 17:54, 27 February 2022 (UTC)
What is pure
substances 2409:4056:191:575B:0:0:2710:A0B1 ( talk) 00:34, 14 May 2022 (UTC)
I have just published some significant edits to the introduction, tagging along with my reasoning here. Broadly, my goals were to improve the readability and understanding here. These included corrections to some inaccurate/misleading information.
Feel free to edit as desired, or commence discussion here. AdmiresCycles ( talk) 06:57, 7 January 2024 (UTC)
Chemicals are products of industry, have a purpose and declared purity. The name is not an abbreviation of chemical substances nor its synonym.
Chemical substances are hierarchically above chemicals. All chemicals are chemical substances, but only some chemical substances are chemicals.
Whoever merged these two articles is clueless and is stomping on established scientific nomenclature just because some people don't understand the difference and say "all chemicals are bad". Lajoswinkler ( talk) 19:40, 22 January 2024 (UTC)