Talk:Chemistry/Archive 1

From Wikipedia, the free encyclopedia

Archive This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

Contents

Overall organization of the article

Does anybody notice that the 'Chemistry' mainpage is absolutely unreadable? Definitions are cryptics. The exact words a definition tries to explain is being used again.

The main page is also becoming nothing more than collection of links to other articles, to which only very little information is added.

Please consider content and readablity before giving up the urge to open new article or parring down definition. There is elegance and there is simplistic.

I agree with you entirely. I'm not sure how it can be rewritten, though. Perhaps we could start with a summary of each of the articles that it links to.
Acegikmo1 05:57, 2 Aug 2004 (UTC)
I agree too, it's only two lists with links to other pages. I thought first "Couldn't there be a section with chemistry history, but then I saw the History of chemistry... I agree with you Acegikmo1, a summary has to be the solution.
The problem of course is that Chemistry is an extraordinarly large and often muddled field with often conflicting theories as well as encompasing almost all of its applications. Although physics is difficult to understand in the end it is simple. Chemistry is not one thing and therefore the need for subdiciplines carrying most of the burden. All we can really get is a definition, i.e. why are all these varied fields called chemistry, and a list of subdiciplines. Chemistry includes large swaths of physics, materials sciences, geology... everything. That's why it's called the central science. I like the fundamental concepts section and the subdiciplines section as they are. Maybe a short summary of the history would be good with a link to the main article. I mean we can only fit a very elementary introduction to chemistry here. Maybe that is the section needed. A layman's terms introduction!!

There should be an article called chemical substance. Andres.

Howabout a redirect to the existing Chemical_compound? Stewart Adcock 00:07, 17 Nov 2003 (UTC)
I think it would be that much more usefull to have one principal article/subsection in main page describing how chemistry view/organize the notion of matter (compounds, susbtance, mixture, elements, molecule, atoms...etc) then from there obscure definitions that need elaborations are put on seperate page. Otherwise we will have myriads of small pages that doesn't give coherent picture. It's very hard to read a page with plenty of links to small definition but no narration. Any thought?


You all can add more information to separation of mixtures.


Anybody interested in contributing to the page Colors of chemicals which is currently rather shabby ???

Hoping that a few chemists may notice this here... This article links to Chemics, which I'd never heard of. Reading the article, it is basically supposed to be where chemistry meets other fields of study. I have never heard this term before, and I am a working chemist. Has anybody else come across it? Would anybody like to be a peer-reviewer, to back me up in suggesting that that page should be deleted? Iridium77 22:41, 26 Jun 2004 (UTC)

             It's a duplicate. SOmebody better erase that page.
They did, and redirected it to Chemistry Iridium77 08:52, 2 Aug 2004 (UTC)


Definition

Anybody else think the initial definition of chemistry is really poor? We fixed the correspondingly poor definition of physics (formerly: "the science of energy and its interactions with matter"). Describing chemistry as the science of matter is overly broad: quarks, muons, and the Z0 particle are "matter" but decidedly not within the domain of chemistry.Scrutchfield

Well nuclear chemistry rarely deals with molecules but is not called arbitrarily called chemistry. Quark and muon interactions are often written in a fashion so as to equate them with chemical reaction. The current description of physics is equally poor if not poorer ("the study of everything") -- because it gives a terribly misleading picture of what physics is. In fact the suggestion that chemists only study molecules (as is given on the physics page) is also pretty bad; since chemists often study supramolecular interactions as well as nonmolecular forms, such as metals. The emphasis on this definition is that chemists care deeply about the identity of the matter, whereas physicists tend to care more about the energetics and generalizability of interactions, with less emphasis on identity. People at the interface (such as physical chemists, or chemical physicists) are, when you use that sort of distinction, somewhere in between.

Agreed that the interactions of fundamental particles are often described in a manner reminiscent of chemical reactions; nonetheless, they are not chemical reactions nor are they within the domain of chemistry. Therefore I think the current definition of chemistry as the science of "matter" is overbroad. Perhaps a better definition would include reference to the fact that chemistry is primarily concerned with the interactions of "normal" atomic matter (not, e.g., dark matter, neutron star matter, etc.) at the supranuclear scale? Scrutchfield

It looks like the first sentence of the opening definition was plagiarized from Merriam-Webster? (See http://www.m-w.com/dictionary/chemistry). Also I respectfully submit that the second sentence is pretty poor. "Chemisty also investigates its interactions with energy and itself"? What does that mean?

Scrutchfield

I took a shot at cleaning up the opening paragraph, what do you think? Jawz 08:28, 16 January 2006 (UTC)


I think the nuclear chemists might be a bit offended by some of this discussion. Yes, nuclear reactions are not chemical reactions we know that. Although chemists are interested in the properties of mostly normal atomic matter I think that to declare quarks as not in the relm of chemistry is ridiculous, they are after all a critical component of all atomic matter. Maybe chemists should abandon the periodic table, afterall the only difference between elements is "nuclear". Just as light is not matter yet is very important to chemistry, not alone but as part of a system. Many nuclear chemists are very interested in quarks and beta particles because they can change the element present. They just are not central to the question being addressed. Nuclear stability is also an important characteristic of each element.
Including organic and inorganic substances seems rather clumsy. Also there are mentions of rather specific things in the definition such as redox chemistry?? We should keep this a pure definition and leave the further explanation to the introduction. I would like to propose a new definition that hopefully adresses all concerns:

Chemistry is the science of matter at or near the atomic scale. In this pursuit chemistry deals with the properties of such matter, the interactions of matter with other matter and the interactions of matter with energy. Chemistry primarily studies atoms and collections of atoms such as molecules, crystals or metals that make up ordinary matter.


I will leave this open to discussion for a while since it seems that others have put thought into this but if I do not hear objections I will change it.

I think your proposed definition is better, and I agree that it makes no sense to mention organic and inorganic substances and electrons at that point. However, you are not mentioning two fundamental concepts explicitly: structure and change. My typical one-sentence definition is: "Chemistry is the science that studies the structure, properties, and transformations of matter at the atomic level." The term "interactions" as you use it is a bit vague, as matter can interact with other matter and energy in ways that would rather be considered physical, such as gravitation. Itub 23:10, 2 March 2006 (UTC)


I guess I was trying to include non-covalent interactions which have become an increasingly important part of chemistry recently. I'm not sure that such interactions fit well into structure, properties or transformations; although each of those plays a role. I also think properties is more fundamental than structure. Structure is more of a result of our efforts to understand the properties of matter. Of course you can argue the other way that structure is the determinant of properties but we are in the end interested in properties not structure. I think interjecting the structure-property relationship here is reasonable as it is fundamental to chemistry. I think that the use of interactions is clear since it is in context "...at or near the atomic scale. In this pursuit..." I think the point of including change is a good one. By the way I also object to the use of molecules in the last paragraph of the current definition, since not all polyatomic chemicals are molecules. How about this:

Chemistry is the science of matter at or near the atomic scale. In this pursuit chemistry deals with the properties of such matter, the tranformations of matter and the interactions of matter with other matter and with energy. Chemistry primarily studies atoms and collections of atoms such as molecules, crystals or metals that make up ordinary matter. According to modern chemistry it is the structure of matter at the atomic scale that is determinant of the nature of any given matter.


Since there has been no further ojection I have changed the definition. Please discuss further changes and improvement here. For the sake of discussion and tranparency I have included the previous definition below and a record of the current definition if more changes are to be made:


Previously: Chemistry (derived from the Arabic word kimia, alchemy, where al is Arabic for the) is the science that deals with the properties of organic and inorganic substances and their interactions with other organic and inorganic substances. In the study of matter, chemistry also investigates the movement of electrons (see energy, physics, biology). Because of the diversity of matter, which is mostly composed of different combinations of atoms, chemists often study how atoms of different chemical elements interact to form molecules and how molecules interact with each other.

Current new defintion: Chemistry (derived from alchemy) is the science of matter at or near the atomic scale. In this pursuit chemistry deals with the properties of such matter, the tranformations of matter and the interactions of matter with other matter and with energy. Chemistry primarily studies atoms and collections of atoms such as molecules, crystals or metals that make up ordinary matter. According to modern chemistry it is the structure of matter at the atomic scale that is determinant of the nature of any given matter.

Someone changed "at or near the atomic scale." to "stemming from differences at the atomic scale." This has been reverted pending further discussion. Personally I think this, while essentially true, is awkward , confusing and unnecessary. It think the fact that different matter differs at the atomic scale is quite well stated later in the definition. Trying to fit every aspect of chemistry into the first sentence will not lead to clarity. Although I see that it is addressing an important reason for the existance of chemistry I think it is much better to keep each sentence simple and accurate while building ideas. Not that I think we should do this since it is covered later but I would be more supportive of a second sentence reading "Chemistry has shown that ordinary matter is composed of atoms and collections of atoms whose variations in structure and composition are critical to the nature of all matter." But I think all of that is included in the second sentence and last sentence. Perhaps we need to have more sentences that are simpler and clear, but not complicated sentences that are redundant. Here is an alternative definition (I think bringing the last sentence up to second is a good idea in terms of flow and clarity but again the overall definition is unchanged):

May 2006

Chemistry (derived from alchemy) is the science of matter at or near the atomic scale. Chemistry has shown that ordinary matter is composed of atoms and collections of atoms whose variations in structure and composition are critical to the nature of the matter. In the pursuit of studying matter chemistry deals with the properties of different matter, the tranformations of matter into new forms of matter and the interactions of matter with other matter and with energy. Chemistry primarily studies atoms and collections of atoms such as molecules, crystals or metals that make up ordinary matter.

What do you think?

Here is the definition from the chemistry portal page that used to be here a while ago. I don't think it is so bad. IMO the second and third sentences are weak and somewhat poorly written and the points being made are in the current chemistry page definition.

Chemistry is the science of matter that deals with the composition, structure, and properties of substances and with the transformations that they undergo. In the study of matter, chemistry also investigates its interactions with energy and itself (see physics, biology). Because of the diversity of matter, which is mostly in the form of atoms, chemists often study how atoms of different chemical elements interact to form molecules and how molecules interact with each other.

  • Latest definition July 17 2006:

Chemistry (derived from alchemy) is the science of matter at or near the atomic scale. Such matter includes atoms and collections of atoms (such as molecules, crystals, and metals) that constitute materials encountered in everyday life. Chemistry deals with the composition and statistical properties of such structures, as well as their transformations and interactions. According to modern chemistry, the physical properties of materials are generally predictable from their structure at the atomic scale. Chemistry is, along with physics, one of the most fundamental natural sciences.

Some changes reverted, some kept. "Chemistry is the science of interactions between matter at or near the atomic scale" is not correct because chemistry also involves the interaction between matter and energy. I'm not sure what "multibodied atomic structures" are and I would also say this is incorrect since we must be careful to include nuclear chemistry as well a sodium ion interacting with chloride ion (aqueous phase). Overall I am not sure that the current revision is better than the May 2006 version. The one point that I did feel was an improtant improvement was the inclusion of "statistical properties" since chemistry is often studied in this way, stat mech e.g. On the structure function relationship I prefer "critical to the nature of the matter" rather than "generally predictable" because we really aren't that good at predicting beyond very fundamental aspects. The lay reader will be misled by this statement into thinking that we can predict many things that we really can't due primarily to complexity. The relationship is valid just our ability to predict is limited to simple systems.--Nick Y. 16:45, 17 July 2006 (UTC)

Introduction

I have removed "It is more accurate, however, to consider chemistry coequal with physics in supporting biology." from the introduction. I don't think we should be addressing which science is better and I think the geologists that use chemistry proabably don't think that chemistry's only role is in supporting biology.

I Also changed "According to contemporary chemists, almost all matter consists of electrons, elements or atoms, ions, molecules or crystals." to "According to contemporary chemists all ordinary matter consists of atoms or the sub atomic components that make up atoms. Atoms may be combined to produce more complex forms of matter such as ions, molecules or crystals. The structure of the world we commonly experience and the properties of the matter we commonly interact with is determined by properties of chemical substances and their interactions." Since crystals, ions and molecules aren't really a fundamental component of matter.

Picture

A chemist

I removed the disturbingly misrepresentative photo (right) which previously headlined this article, primarily because it shows a "chemist" working without taking even the most basic safety precautions (e.g. no eye or skin protection whatsoever). When I worked in a university chem lab as an impressionable undergraduate, I would have been summarily booted had I attempted to do what was depicted here. -- Seth Ilys 13:29, 10 May 2004 (UTC)

I'm the one who had added that pic. I guess I agree with you. I'll look for a better one. Quadell 13:36, May 10, 2004 (UTC)

Do any of these look good? Quadell 13:49, May 10, 2004 (UTC)

The pic now looks good.But I feel, the description is inappropriate!(i.e. it would do better without the title 'a chemical reaction') Its better without the name.Image:Oxidation_of_hydrogen_gas.png


uhm, guys... Is it me or these pictures are not necessary? I know it looks pretty but we have to remember a lot of people are trying to fit these encyclopedia on a limited memory. Shouldn't we limit picture to 'absolute necessary' item? (Diagram, illustration, equations)

The first one looks appropriate Quadell!. I did not add that coz i dint know whether they were copyrighted.:SudhirP 04:26, May 12, 2004 (UTC)

They are all public domain. I'm adding pic 1 to the article (as an addition to, not replacing, the test-tube pic). Quadell 12:30, May 12, 2004 (UTC)

The test tube is ok, but the scientist is a more clear representation of chemistry (study). Bensaccount 16:43, 15 May 2004 (UTC)

C'mon, there's gotta be somebody here who works in a lab - go take a picture of it! (Or sneak into someone else's lab :-) ) Stan 04:47, 18 May 2004 (UTC)
Most labs are suprisingly uninteresting places. And why is a lab representative of chemistry anyway? Most chemistry is done in industrial facilities. I don't think that we need a cheesy pic on the front page, so I've taken it off as part of the major edit that I've just done.
I still have some issues with this page. I want to shorten the "fundamental concepts" section somewhat, perhaps in the same way that I just did to branches of chemistry. There is no point duplicating information when it only makes the thing harder to navigate. Succint points, yes. Large paragraphs, no.
Iridium77 11:45, 19 May 2004 (UTC)
Pictures of labs are maybe uninteresting to you, but consider high-school students in Gabon - to them a firsthand look at where chemistry is done would be completely fascinating, maybe even inspire them to study it further. A picture of an industrial facility wouldn't come amiss either. Stan 13:22, 19 May 2004 (UTC)
But what is the point of a picture of a lab? The kind of lab that one does synthesis in is one thing (usually a smelly, dirty place), the labs that the physical chemists use look totally different, analysts have something different again, perhaps the most chemistry is actually done in a library.
My point is this: the article is about chemistry, and chemistry is a whole lot more than a picture of a lab or a refinery or whatever. Chemistry is about knowledge, not about some guy in a white coat looking studious.
There's a decent picture of a workstation at a lab under laboratory, which in my opinion is where it should stay. Chemistry is not what happens in a lab, chemistry is understanding what happens in a lab.
Iridium77 19:00, 19 May 2004 (UTC)

I changed "scientific study" to "science". Science refers to the systematic acquisition of new knowledge about nature and the body of already existing knowledge so gained. Bensaccount 01:46, 18 May 2004 (UTC)



Chemical Notation

How write a chemical formula

i.e.

O = C - R in threedimensional form ( with oxygen over the C and = ).

and more complex ones ???.

You could try TeX_markup. I've never used it though, so I don't know if that would help. The village pump is a good place to ask things like this. Angela 13:54, 2 Aug 2003 (UTC)
That's all but impossible, even using TeX Markup. I personally use a separate program (ChemSketch), which works well for just about everything. The pictures of acetonitrile, acrylonitrile, etc. are drawn using it.

Isn't there a more easy way to write MnO4- than

MnO< sub>4< sup>-? Such as MnO,,4,,^-^?

Hmm... try this:

MnO_4^-

Of course, that does create a picture sometimes, but... :-\ ugen64 02:23, Nov 17, 2003 (UTC)


If you check the lidocaine page, it gives the chemical formula as C14H22N20 HCl H2O. That's fine, except I'm wondering where the HCl and H2O came from. Are they inherently present in lidocaine? If so, how? Are they somehow attached (which is impossible, considering the formula)? I've drawn lidocaine's structure on ChemSketch, and will upload it soon, but I don't have the HCl and H2O anywhere...? ugen64 02:22, Nov 17, 2003 (UTC)

Lidocain is often supplied as the HCl salt. The HCl is not bonded to the main drug molecule directly. The H2O is a hydrate, which will be loosely attached, probably through hydrogen bonding. Iridium77 22:31, 28 Mar 2004 (UTC)

Category

Category:Chemistry now has 172 articles in the main category. Many of these should be put in subcategories and taken out of the main cat. I don't know much about the subject. I'd appreciate any help.

Also, I created Template:Chem-cat to ask for help with this. But it has been listed at Wikipedia:Templates for deletion. Maurreen (talk) 23:05, 13 August 2005 (UTC)

Chemical nomenclature - should this be linked?

I have unlinked Chemical nomenclature, as its content is repeated in full in the summary below. It still serves as a useful disambig page, but unlike the other "Main articles" it does not contain any new content. If you disagree, feel free to revert, but I'd be curious what your reasoning is. Thanks to all who helped build this excellent article. JesseW 06:02, 17 August 2005 (UTC)

History of Chemistry summary?

Do people feel that a summary of the History of Chemistry article would be valuable in the same-named section? I'll get to writing it, but I wanted to leave some time for people to comment on my change above, so I thought I'd ask for responses first. JesseW 06:09, 17 August 2005 (UTC)

Yes a nice very short summary would be good.

tmcsherry- Your changes seem out of place in the History section. They seem more appropriate in the Bohr model article.--Nick Y. 16:55, 18 July 2006 (UTC)

Nonexistent Wikiportal

Umm... as I ran into this article, I noticed that the first (and most prominent) link is that for the Chemistry portal. That would be perfectly fine, but the only problem is that it is a redlink. Shouldn't the link be made until the portal is up and running? --Titoxd 22:43, 26 August 2005 (UTC)

The portal is running now. The link should be good. ~K 18:51, 5 October 2005 (UTC)

supernatural?

Hello, there is a content dispute at Methodological naturalism that I've filed an article RFC for [1]

The original question is whether or not the scientific method is a natural method or a supernatural method of scientific investigation. One editor (Markus Schmaus) refuses to allow the scientific method be listed as a natural method unless a link can be provided to support the claim. I assume he is a proponent of Intelligent Design which pushes the view that ID is "scientific" even though it investigates supernatural causes such as how God must have creaeted life on earth. I assume it is this POV that is getting pushed, and Schmaus will not allow the scientific method be listed as an example of MN because then ID would not fit in the scientific method.

In an attempt to resolve the dispute until some sort of consensus was reached, I removed the mention of the Scientific Method as an example of methodolgical naturalism and instead inserted "astronomy, biology, chemistry, geology, and physics" are examples of methodological naturalism. Schmaus is now disputing that these are examples of MN and insists on a URL to prove that they are natural methods rather than supernatural methods of scientific investigation.

[2]

Since methodological naturalism is a minor article with only a few editors, the dispute has remained unresolved for lack of any sort of consensus. Please weigh in with your comments at the following links:

Scientific method is natural or supernatural

astronomy, biology, chemistry, geology, and physics are natural or supernatural methods

If you have links to support whether it is supernatural or natural, that would be greatly appreciated. FuelWagon 18:11, 14 September 2005 (UTC)

Bizarre paragraph added

The bizarre paragraph was just added:

The greek origin of chemistry was derived from the word "kemet", which means black. In this case, this refers to the black skin of the earliest denizens of black Egypt. Black Egyptians were renowned in the ancient world for their advanced technological knowledge. One hieroglyph even showed the construction of a helicopter-UFO hybrid [3].

I removed it from the article for now. Can anybody verify this? ~K 18:54, 5 October 2005 (UTC)

It isn't bizarre, it's the truth that has been suppressed by the white-dominated world-view for more than a few millenia at least. See [4] for details. Blackpower 19:41, 5 October 2005 (UTC)

The bizarre thing about that paragraph is not that the Egyptians were the first ones to explore chemistry - their early scientific achievements are a well established fact. But I'm not very sure about that helicopter-tank-ufo link, indeed it looks like a lot of esoteric science-fiction rubbish to me, so perhaps it should better be removed.


I think this is an issue best addressed in the alchemy section. If anyone is going to make any major changes to the alchemy section please discuss it in the discussion section and let us know what you have changed. Wikipedia is a place for facts not that there is not room to represent that there remains significant debate or disagreement. The facts are that to the best of our knowledge from the texts that were translated into arabic and then into latin from the library at Alexandria an outstanding amount of relatively advanced knowledge in the ancient world has Egyptian origins however the origin of the word chemistry is less clear.


"The word alchemy comes from the Arabic al-kīmiyaˀ or al-khīmiyaˀ (الكيمياء or الخيمياء), which is probably formed from the article al- and the Greek word chumeia (χυμεία) meaning "cast together", "pour together", "weld", "alloy", etc. (from khumatos, "that which is poured out, an ingot").
Some believe that the Arabic word al-kīmiyaˀ means "the Egyptian [science]", borrowing the Coptic word kēme (or from the mediaeval Bohairic dialect of Coptic, which wrote the word khēme), meaning "Egypt". The Coptic word derives from Demotic kmỉ, itself from ancient Egyptian kmt. The ancient Egyptian word referred to both the country and the colour "black" (Egypt was the "Black land", by contrast with the "Red land", the surrounding desert), so it is thought that such a borrowing in Arabic was appropriate for "Egyptian black arts". However, a decree of Diocletian, written about 300 CE in Greek, speaks against "the ancient writings of the Egyptians, which treat of the khēmia [transmutation] of gold and silver". The Arabic therefore could derive from a purely Greek word, not Coptic, and have been later connected with ancient Egypt through what linguists term a "folk etymology."


I don't think that this is in anyway a misrepresentation of the best knowledge we have about this subject. The egyptian use or contact with U.F.O.s is very clearly an issue of debate and has no place in a chemistry or alchemy section however it could be relevant in the Unidentified flying object section.


publication

would you like to publish this article? -- Zondor 22:16, 27 November 2005 (UTC)

Etymology

There is an apparent incosistency in the etymology of the words Chemistry and Alchemy as describes in the two Wikipedia lemmas. The Chemistry lemma states that "Chemistry (derived from the Arabic word kimia, alchemy, where al is Arabic for the) is the..."

while the Alchemy lemma states that "The word alchemy comes from the Arabic al-kīmiyaˀ or al-khīmiyaˀ (الكيمياء or الخيمياء), which is probably formed from the article al- and the Greek word chumeia (χυμεία) meaning "cast together", "pour together", "weld", "alloy", etc. (from khumatos, "that which is poured out, an ingot"). A decree of Diocletian, written about 300 CE in Greek, speaks against "the ancient writings of the Egyptians, which treat of the khēmia [transmutation] of gold and silver".

The etymology of the word Chemistry has been a matter of debate for decades, and I believe that one should write in both lemmas that there are two main origins of the word Chemistry, the Greek and the Arabic one, with the Greek - in my view - being much more credible. Indeed in the word "Χημεία" (Modern Greek for "Chemistry") used to be written as "Χυμεία" in Byzantine times. Ioannis, PhD Chemistry--195.134.76.249 14:12, 10 January 2006 (UTC)

Agreed. CarlGH 07:50, 19 April 2006 (UTC)
  • chemistry etymology should have an article of their own shared with the alchemy people. one of my sources favors both the Egyptian word for black as in black earth and the Greek cheo for pouring and casting etc. See A History of Chemistry Bernadette Bensaude-Vincent, Isabelle Stengers and another source also relates it to Khem See discussion there ref: Chemical History Tour, Picturing Chemistry from Alchemy to Modern Molecular Science Adele Droblas Greenberg Wiley-Interscience 2000 ISBN 0471354082 V8rik 20:14, 13 January 2006 (UTC)

Electrochemistry page...

the electrochemistry page is messed up... somebody fix it!!

Etymology again

The etymology section of this article is about the etymology of alchemy instead of chemistry. "Chemistry" is a derivative from "alchemy" as alchemists are called chemists in short form, then a "-try" is added to this to make "chemistry". --Deryck C. 16:06, 14 May 2006 (UTC)

Definition Again

There seems to be continuous change to the definition such that it wobbles around being accurate but only is for short periods of time. The most recent iteration on this is once again the exclusion of monatomic species from chemistry. Please lets not make the same mistakes over and over again. The periodic table is essential to chemistry and so are the elements. Many chemists, to this day, work with monatomic elements both in theory and in practice, let's not leave them out of our definition. I have weakly edited the definition to reflect this with as little change as possible.--Nick Y. 23:25, 25 August 2006 (UTC)

Introduction

The newly introduced or expanded phase paragraph seems a little too long for the introduction. Phase changes may be a good example but leave the details for the proper article.--Nick Y. 17:18, 28 August 2006 (UTC)