Talk:Allotropy

Comments

In the first paragraph, should graphene be considered a different allotrope of graphite? Or simply a smaller crystal of graphite constrained from vertical growth. —Preceding unsigned comment added by 24.240.34.25 (talk) 05:51, 4 May 2011 (UTC)

Clearly, steam, water, and ice are not allotropes. However, what about the various solid phases of water (ice(I), ice(II), etc...)? I believe they would be considered polymorphs, but probably not allotropes because water isn't a pure element. Is this correct? --Matt Stoker

Right. Allotropy refers specifically to elements. I double-checked my understanding of this with the Penguin Dictionary of Chemistry (DWA Sharp, Penguin:1990 ISBN 0-145-051232-2), but I'd encourage anyone to consult whatever credible reference they feel necessary. --JoeAnderson

The last edit of this page commented "allotropy and isomerism are *distinct*" -- yes, but how? Roughly, is it the case that two allotropes will have completely different chemical properties (diamond vs carbon), while isomers tend to have similar properties (similar boiling points, etc)? -- Tarquin, Sunday, July 7, 2002

It is suggested that we consult the MACMILLAN ENCYCLOPEDIA of CHEMISTRY edited by J.J.Lagowski, 1997, SIMON SCHUSTER for a definitive exposition of the subjects ALLOTROPES and POLYMORPHS. It is pointed out that there is no phenomenon that results in the existence of ALLOTROPES. Allotropes exist as a result of the differing chemical bonding of the same atoms. --Anon

Why is "allotropy" a misnomer? -phma

The first paragraph of this article needs to be clarified. 207.67.132.210 13:42, 17 January 2006 (UTC)

This article indicates that allotrops can exist in the the solid, liquid, or gas phases. Is this true? I have been led to believe that allotropy specifically relates the structure of the solid matrix. for example for Fe: alpha-ferrite (BCC) gamma-austenite (FCC) delta-ferrite (BCC) are all allotropes > However, I have not been able to find information confirming nor contradicting this. The text I am using as a reference is Structures and Properties of Engineering Alloys Second Edition by Smith ISBN 0-07-059172-5

Yes, those phases would be allotropes, but only when talking about pure iron. In metallurgy, it's generally preferred to use the term "phase" as opposed to "allotrope" to avoid ambiguity. Allotropes are distinct chemical species with varying reactivities and physical properties. Allotropes can be present in any phase, but some become unstable in certain phases and will transition into a more energetically favourable structure. Hope this helps. --Xanthine 00:10, 1 May 2006 (UTC)

Allotropy - isomers

The term allotropy is usually only used for elements. In the case of compouds, the analogous term would be isomers. Andreas 02:25, 26 January 2006 (UTC)

Expert

What exactly needs expert attention? kotepho 01:57, 25 March 2006 (UTC)

Erm... For a start, until recently the definition said a lot more about what allotropy isn't than what it actually is... --Xanthine 23:11, 30 April 2006 (UTC)

Major Cleanup

I believe I'm suitably qualified to be an expert on this subject. I have done a large scale cleanup of this article, tidying up any discrepancies and clarifying a number of points. I think it reads a lot better now. If you notice any errors (factual or grammatical), please do let me know. And feel free to correct them. --Xanthine 00:10, 1 May 2006 (UTC)

Usually ...

The article illustrates allotropy with two crystalline forms of Fe, but my impression is that usually allotropy refers to molecules or low dimensional materials. It can be assumed that all elements exhibit polymorphy, especially at high pressures. So while formally allotropy (isomerism for elements) is widespread, for instructional purposes, the discussion is usually limited to species existing as molecules (S, Se, As, P, C, O).--Smokefoot (talk) 13:09, 20 December 2007 (UTC)

Molecules or covalent solids (diamond is not a molecular solid, unless you call the entire crystal a very big molecule!) But I've never seen the term applied to metals. --Itub (talk) 16:37, 20 December 2007 (UTC)

I just found that many books do speak of allotropes of iron.[1] These are often books on metallurgy and related topics. It is true, however, that most general chemistry textbooks only seem to give examples of allotropy among nonmetals. --Itub (talk) 09:58, 9 January 2008 (UTC)

References for metals

Are there any references for the metal allotropes? Even in the crystallography open database and the inorganic crystal structure database there is no structure for strontium other than the cubic. 129.93.61.170 (talk) 15:19, 19 August 2008 (UTC)Jared Hansen

Definition of Allotropy??????

It is saying that in the definition the word "chemical elements", but silica (SiO2) is not a element. But it has allotropic forms??????????? —Preceding unsigned comment added by Shivaaprs (talk • contribs) 03:24, 10 July 2010 (UTC)

The article refers to the element silicon (Si), not the compound silica which is the short name for silicon dioxide (SiO₂). Dirac66 (talk) 12:27, 10 July 2010 (UTC)

Allotropy vs polymorphism

User 201.235.24.69 today added a [who?] to ask who are the many other chemists who have repeated Ostwald's advice to replace the term "allotropy" by "polymorphism". The sentence which is questioned was added by me on 18 May 2007. It is a paraphrase of Jensen's 2006 article, which refers to "sage advice, which many have since repeated", with a reference to a 1964 book "The allotropy of the elements" by W.E. Addison. I will add a reference to indicate the source of this sentence and the word "many", even if Wikipedia does not identify the many. Dirac66 (talk) 00:31, 1 February 2012 (UTC)