Talk:Molecule/Archive 1

Question

Do any Atoms and Molecules(?) stick to each other WITHOUT heating above 200 degrees F.

ANWSER: YES NO

THERE ARE: FEW MANY

Were(?) can I find the details.

How do you break ELECTRON BONDS, just methods used (passing one molecule over another (at room temp, while heating them))? I do not need to know the exact proccess.

thanks - Anonymous

Certain atoms and molecules (technically, atoms fall into the class of molecules) will combine without heating. They can simply be put close to each other (i.e.: mixed in liquid, air passing over a solid, etc. whatever), although there must be some heat, such that it is not absolute zero, because if it's absolute zero the molecules are not moving, but absolute zero cannot be achieved according to the laws of thermodynamics. The question of whether there are "few or many" is rather vague. It could be a question of how many types of molecules will combine without heating and under what conditions, or it could be a question of how many molecules in the Universe or on Earth can do this, but it's not that useful a question anyway.

The bonds between atoms in a molecule can be broken by inducing atoms to bond instead with another molecule by just putting them together, in the same way as above, or by adding some energy to the molecule, like light or heat, so that the bonds break.

In all cases, the exact temperature for every reaction might be different depending on the molecule, so one cannot say universally that all reactions will take place "at room temp" or not, or whatever. I suggest you pick up a basic General Chemistry textbook and check it out. Note also that the way the universe actually works is probably more crazy than you have ever imagined. - Centrx 05:58, 23 Dec 2004 (UTC)

macromolecules

From the article: "An example of a macroscopically-sized molecule is DNA, a macromolecule" Being a macromolecule has nothing to do with being macroscopic. You could manufacture a DNA molecule that was long enough to become a macroscopic object, but must DNA molecules are microscopic objects. Memenen 14:21, 27 Dec 2004 (UTC)

• Good point. I have edited the DNA example. Does is sound good? --Unconcerned 05:49, 28 Dec 2004 (UTC)

Intro Paragraph

Abstractly, a single atom may be considered a molecule, as it is when referred to collectively with molecules of multiple atoms, but in practice the use of the word molecule is usually confined to chemical compounds, of multiple atoms.

I am removing this from the article -- Not only is it confusing, but it contradicts the preceeding definition of molecule (two or more atoms, or before a previous edit, multiple atoms). Tygar 06:55, Feb 25, 2005 (UTC)

This is an older discussion. By definition, molecules -- the smallest particles of a compound that still preserve its chemical and physical properties -- can consist of one atom or more atoms bonded together. It is still a valid definition that can be found in most, if not all, chemistry and physics textbooks. A peculiar use of the term molecular is as a synonym to covalent, which probably arises from the feeling that ionic bonds do not usually yield well-defined "smallest particles" consistent with the definition above. However, a whole chapter of physics, dealing with thermodynamics and the kinetic theory of gases, consider monoatomic gases as composed of single-atom molecules (examples: monoatomic+molecule and monatomic+molecule). Therefore, I feel that the article should include all aspects of the subject discussed as opposed to just a peculiar one and as such re-included the fragment above. The discussion remains open, though.--Unconcerned 17:33, 30 Mar 2005 (UTC)

Avogadro's Law is stated a couple of times in the Wikipedia [1] & [2]

"equal volumes of gases, at the same temperature and pressure, contain the same number of molecules"

Therefore the noble gases (He, Ne, Ar etc) are made up of atoms that can also be described as monatomic molecules. There are intermolecular forces of attraction between the atoms of noble gases and they follow all the gas laws as do other simple molecules.

I agree with Unconcerned.

Aren't those forces then not rightly called intermolecular but instead interATOMIC interactions? I think something needs to be added that recgnizes the EXTREME obscurity of using the term "molecule" to refer not to atomic combinations but to individual atoms. --Deglr6328 01:53, 17 July 2005 (UTC)

It iswas already there in the second para of the intro: "The concept of monatomic molecule is used in the kinetic theory of gases." Monatomic meaning single-atom.--Unconcerned 04:02, 17 July 2005 (UTC)

I have scrambled the paragraph a bit to emphasize on this only use of the monatomic concept, hope this sounds clearer.--Unconcerned 04:13, 17 July 2005 (UTC)

DNA Example

I believe that the DNA visibility example is useful in providing a feeling about the size and tangibility of molecules, and in making the concept less abstract. The way it was formulated also allowed for a few useful wikilinks. Therefore, I re-included the removed fragment.--Unconcerned 17:33, 30 Mar 2005 (UTC)

To Do / Wish List

1. Discussion on how spectroscopy methods are used to ellucidate molecular structures
2. History: description of first evidence that molecules existed

edits from user:202.141.141.10 / user:Hallenrm

I have reverted the edits from user:202.141.141.10 for the following reasons:

• Definition
  • I'm not aware of any recent change in the definition of a molecule
  • A molecule cannot be "the smallest particle of a pure substance that is made up of more than one atoms" -- that would be a biatomic molecular fragment
  • Molecule is a concept with a far wider usage than just molecular physics/chemistry; confining the general definition to the specifics of a particular field is not in line with a general encyclopedia article

A molecule can not be equated with a chemical substance, a chemical substance is an enseble of molecules. Thus to define molecule as the smallest particle that retains its chemical properties is erroneous. History cannot be a justification for erroneous definitions. Stictly speaking, the properties of an ensemble cannot be the same as those of any individual members of the ensemble.

Please cite references wherein Molecule is a concept with a far wider usage than just molecular physics/chemistry. I do not find any such reference on the page "molecule" in wikipedia. Charlie 07:44, 14 December 2005 (UTC)

Chemistry, biology, physics --in general; then engineering whenever the stoichiometry of a certain chemical process becomes involved; science and engineering in general do not look at a molecule as the solution of Schroedinger's equation, but rather as an entity defined through a simple statement separating it from other entities such as molecular fragments --radicals or ions.

You insist upon stating that a molecule is "the smallest particle of a pure substance composed of more than one atom". Take for example the substance benzene; the fragment CH is the smallest particle of benzene that is composed of more than one atom. Yet, CH is not a molecule, and particularly not a benzene molecule. Your definition is flawed and therefore should not replace a perfectly valid one.--Unconcerned 17:44, 14 December 2005 (UTC)

• Molecular structure
  • I see no reason for deleting this fragment: "A pure substance is composed of molecules with the same geometrical structure" -- any reason why this wouldn't be true?
  • The phrase "equilibrium geometries" is similar to "averaged out"; the article molecular geometry gives the necessary details about how this works

• Molecular spectroscopy
  • Molecular spectroscpy deals specifically with the response of molecules to various probing signals; "interaction of pure chemical substances, elements or compounds, with various electromagnetic radiations, electrons or positrons." includes a multitude of other phenomena not necessarily specific to molecular spectroscopy (e.g.: atomic spectroscopy, excitation, ionization, abstraction etc).

I felt these explanations were necessary since user:202.141.141.10 seems to have complained in the past about other editors' conservatorism.--Unconcerned 10:54, 13 December 2005 (UTC)

Strictly speaking few molecules of an ensemble of molecules that constitue a sample of a pure substance would have the same geometry at any instant of time. So, to say that "A pure substance is composed of molecules with the same geometrical structure" would be inaccurate to say the least. The phrase "averaged out" is more easily understood by a non expert (chemist or physicist) than the phrase "equilibrium geometries". Wikipedia is not only for experts, who anyway may be familiar with the jargon but other novices too.Charlie 07:33, 14 December 2005 (UTC)

Please read this phrase again: "Molecules have fixed equilibrium geometries[...]". It never stated that all molecules have the same instantaneous geometry. A pure substance is composed of identical isomers of molecules with the same chemical formula. Isomeric molecules are molecules with the same (equilibrium) geometry. You don't suppose this definition is also obsolete, do you?--Unconcerned 17:44, 14 December 2005 (UTC)

It is a classic case of obfusication in science, why can't thoing be stated in as easy terms as possible, "equilibrium geometries" is a phrase that I seldom encountered in all my education in chemistry, and that is, upto a doctrate in a premium institute.Charlie 07:15, 15 December 2005 (UTC)

The attitude of the Unconcerned is what I call conservatism, being not ready to see any other idea that is not his own. Mature adults, which I presume he/she is must be a bit more responsive.Charlie 07:22, 15 December 2005 (UTC)

A quick check: try a google search for the phrase "molecule equilibrium-geometry +.edu". As of today, 12/15/05, it yields about 60,200 positive results. Hope this helps :-) --Unconcerned 09:51, 15 December 2005 (UTC) Also check definition from IUPAC --Unconcerned 10:35, 15 December 2005 (UTC)

Since you are questioning my maturity and responsivity, please take your time to answer these three specific questions before reverting perfectly valid statements into questionable ones. Thanks and please check out below:

more than one atom

Dr. Hallen, I am copying a question I have asked of you above, and you still have not answered. Please check below: --Unconcerned 09:12, 15 December 2005 (UTC) ::You insist upon stating that a molecule is "the smallest particle of a pure substance composed of more than one atom". Take for example the substance benzene; the fragment CH is the smallest particle of benzene that is composed of more than one atom. Yet, CH is not a molecule, and particularly not a benzene molecule. Your definition is flawed and therefore should not replace a perfectly valid one.--Unconcerned 17:44, 14 December 2005 (UTC)

I've grouped all possible definitions in a single paragraph, and included a few external links in support of each def. --Unconcerned 12:26, 15 December 2005 (UTC)

kinetic theory of gases

Dr. Hallen, when did in your opinion the kinetic theory of gases abandon the concept of monatomic molecule? From what I know the concept is still very much being used in physics. --Unconcerned 09:12, 15 December 2005 (UTC)

equilibrium geometries

Dr. Hallen, please read through the following two fragments and explain why do you think the first one is not as concise and explicit as the second one? *Molecules have fixed equilibrium (or average) geometries—bond lengths and angles—. A pure substance is composed of molecules with the same equilibrium geometrical structure. *A molecule can be visualized as an entity having a fixed equilibrium geometry—bond lengths and angles— however this geometry is constantly changing in an ensemble of molecules (a sample of a pure substance). Thus, a pure substance is composed of molecules with varying geometries, but averaged out on time it is a geometrical structure.

I've slightly re-worded the molecular geometry section in the hope to capture the idea of average geometry without conflicting with the rest of the paragraph. Please let me know how that works.

Many thanks and looking forward for a fruitful collaboration. --Unconcerned 09:12, 15 December 2005 (UTC)

The changes are indeed welcome. I appreciate the attitude wholeheartedly. Charlie 07:35, 16 December 2005 (UTC)

Question regarding abstract or concrete representation of molecules

This will be an amusing and obvious answer for chemist, but nonetheless important for people discovering the entry of molecule.

Does the structural formula of a molecule represent, at any degree, the concrete, physical form of this molecule? If so, at what level does the shape is more precisely relating to the structural formula?

For example, one of the fatty acid in a phospholipid molecule seems to be a strait line because it is a chain of CH2. Does that mean part of this molecule is actually a real, concrete line(or a lineal form)?

Thanks in advance!

--Enigma 21:11, 26 December 2005 (UTC)

Figure 1 of the article pretty much answers your question. A 2D formula does not tell you much about the 3D structure - at least not if you are not experienced in translating 2D into 3D (although good structural formulas will give you many 3D-hints). As you can see in figure 1, carbon atoms have four bonds in an tetrahedral manner so it is impossible for CH2 chains to build "lines". Instead they will form zig-zag lines which are, however, flexible due to bond-rotation. The best way to get an idea about 3D molecule structures is to use molecule model kits (real ones or computer-based ones). Cacycle 00:48, 27 December 2005 (UTC)

Thanks Cacycle, I appreciate. --Enigma 08:54, 30 December 2005 (UTC)

Also it is important to note that a molecule can be in many different conformations (different shapes without changing connectivity) and be the same molecule. In fact most molecules are constantly changing such conformations as tmany bonds allow for rotation.

Miscellaneous talk

The definition of a molecule as "the smallest indivisible portion of a substance that retains chemical and physical properties" is widespread among encyclopaedias and vocabularies. However,it looks *very puzzling* to me. Most chemical and physical properties of a substance have sense only when we talk of a *set* of molecules together. For example,I see as plain nonsense asking something like "at what temperature/pressure will that single isolated water molecule boil/ice/melt?". I think no one will deny phase transitions of a substance are among the most basic physico-chemical properties of a substance,but at what number of molecules does this make sense?

You have a very good point. "Physical properties" should not be part of this talk. A molecule of water isn't wet. Nor are two or a dozen. Nor will you get much wave action :).

Most solids of which you're familiar on earth don't even HAVE molecules. A typical rock is a matrix of ions, all jammed together willy nilly. No identifiable "molecules" anywhere. So there are molecules, but we should try in our definitions not to pretend that everything is made up of them, as is true for atoms. In some cases in solids, atoms are grouped into identifiable molecules. In other cases they aren't. The only time you always have molecules is in gases. And there, the "molecule" is the thing flying around with all the space around it, bouncing off other things if the same type. Sbharris 02:46, 11 June 2006 (UTC)

---

Isn't the "word analogy" thingy a little too puerile? I mean, if I follow the paragraph and add carbon atoms (carbon black in a first approximation) to water molecules (tap water in another approximation)... Isn't there any other analogy -- if necessary at all?--Unconcerned 10:08, 19 May 2004 (UTC)

Moved the analogy paragraph on the talk page. Besides, (CH₂O)₃ is not a sugar molecule but rather the chemical formula of a sugar. The analogy might work for chemical formula.--Unconcerned 01:15, 20 May 2004 (UTC)

Molecules are analogous to words. If one adds the letter "e" to the word "can", one obtains "cane". In a similar fashion, if one adds C atoms to H₂O (the water molecule), one obtains (CH₂O)₃ (a sugar molecule).

Bulky caption stuff

I put the following "image caption" stuff here; generally, it's not advisable to try to put a full paragraph in a caption. Rather it's better to describe the caption in the body of the work; I'll leave it here for now.--Sadi Carnot 13:34, 7 April 2006 (UTC)

In the 3D model on the left, carbon atoms are represented by gray spheres; white spheres represent the hydrogen atoms and the cylinders represent the bonds. The model is enveloped in a "mesh" representation of the molecular surface, colored by areas of positive (red) and negative (blue) electric charge. In the 3D model (center), the light-blue spheres represent carbon atoms, the white spheres are hydrogen atoms, and the cylinders in between the atoms correspond to single bonds

Monatomic molecules

A molecule really is the smallest unit of a substance which retains its chemistry. Thus, molecules of elemental He, Ne, Ar, Kr, Xe are monatomic. That's true whether these substances are in the form of gases, liquids, or solids. This isn't only a "kinetic theory of gases" thing; rather it's a general extension of the idea of a molecule as the last division you can naturally make and still retain the same chemical stuff (or the last division you can amplify and get the same chemical stuff). I think the article ought to start out that way, and then note that most molecules contain 2 or more atoms. There should also be mention of the fact that "molecule" has definition problems in many solids: where are the molecules in a salt crystal, a diamond, or bit of graphite? Many common solids aren't really composed of classical molecules. They just aren't! The concept really is a fully natural one ONLY in gases, and it is there of course that some molecules consist only of one atom.

Wiki should be simple, but never so simple as to tell the reader what isn't so. Do you want me to make a first pass at fixing this?Sbharris 02:30, 11 June 2006 (UTC)

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