Talk:Molecule

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WikiProject Chemistry (Rated C-class, Top-importance)
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Archives[edit]

collective, collectiion and diamond[edit]

In the introductory paragraph, aggregate (a total considered with reference to its constituent parts) seems quite a bit more suitable than collection (an accumulation; a deposit) or even collective (this last one was masked vandalism).

As for the diamond "molecule": the term molecule refers to a well-defined particle of a chemically pure substance. Atomically pure diamond yields no well-defined molecular particle anyone could point to. Moreover, a common diamond crystal will always carry lattice and surface defects that make its local chemical properties different than the bulk. Even the most perfect diamond crystal will have surface terminal groups (hydrogens, hydroxyls, carbonyls, etc.) and so it will not be a pure chemical substance overall. It will be a covalent structure, though.

--Unconcerned 07:08, 13 September 2006 (UTC)

Let me be devil's advocate. Assume a perfect crystal with no dislocations. That's possible, and it's even possible on quite large scales. The same is true for single polymer molecules, like the DNA making up a chromosome. Thus, you have one big molecule. As for "pure chemical sustance", this one molecule may be the only exemplifier of whatever chemical substance it is. If so, the word "pure" has no meaning. "Pure" applies when we're considering copies, but we might not, and nothing says we must. Any single molecule is by definition pure. If it's one molecule, and it has a formula, it's a bonafide chemical substance. There may not be another molecule in the universe like it, with the exact same formula. So? That might be true of any of your X chromosomes if they happen to have a unique mutation. Again, so? What is or isn't a molecule is a matter of aesthetics, not science. If they get too big, people don't like to call them molecules, is all. We might as well just admit this, and move on. SBHarris 19:16, 15 September 2006 (UTC)
Agree, but if it gets too big then stability and/or "well definedness" become questionable :-) "Purity" is at its best a rather vague concept. From the general definition standpoint ("the smallest particle...") one could always imagine the most extreme case that fits the description; any grain of sand could eventually be considered a unique, pure molecule, right? Kinetic theory of gases and the molecular vs. continuum treatments set the background for the definition of a molecule based on divisibility. (see [1]) I am being bold and so have added some of this discussion in the intro paragraph. As a side note, a chemist with some molecular modeling experience will definitely feel uncomfortable to accept as molecule a structure that has to be decribed using crystallography-specific "unit cells", or "periodic boundary condition" models. Or one that simply won't entirely fit on a decent computer display ;-) --Unconcerned 07:31, 17 September 2006 (UTC)

Intro definition[edit]

I have been reverted by User:Vsmith (reason: per ref Zumdahl). Thus, I am putting the topic here to discuss further. The intro definition as it stands is:

In chemistry, a molecule is an aggregate of two or more atoms in a definite arrangement held together by covalent chemical bonds.

Not all molecules are held together by covalent bonds, an example being DNA which is held together by hydrogen bonds. Moreover, most supermolecules are held together by non-covalent bonds. It would be correct to say that:

In chemistry, a molecule is a aggregate of two or more atoms in a definite arrangement held together by electromagnetic forces, such as covalent bonds.

This would be all inclusive. --Sadi Carnot 17:33, 17 September 2006 (UTC)

Purists would probably insist that any given strand of DNA consists of TWO molecules, not one. The real problem is that the chemical properties and structure of molecules are determined by other than their covalent bonds (the hydrogen bonds of DNA and those that determine the teriary structures of proteins, etc). If we define molecules chemically, we need to include all kinds of bonds. If we define them physically (as in a gas) we don't require any bonds at all. So the LEAD should continue to consist of paragraphs, each of which gives one of the several different definitions of "molecule" in use by chemists and physicists, under various circumstances. They aren't all the same, and they don't have to be. If we can find ONE definition that fits them all, it's not OUR failing. The word has many uses and meanings, that's all. Sorry, but sometimes science is like that. Definitions change. Doctors still can't agree on what constitutes a "fever"! And they keep changing the definition of "diabetes". And organic chemists can't even agree on whether or not organic compounds have to have hydrogen in them. When this happens, you simply have to summarize conflicting uses and points of view, and pass on. And you reverters, beware. The pure and simple truth is rarely pure and never simple (Wilde). The guy trying to say something additional by adding an expansion, is probably right. SBHarris 17:49, 17 September 2006 (UTC)
Expand, yes. But the basic bonding within molecules is covalent. Add info regarding hydrogen and other bonding in and between supermolecules, but the basic starting definition differentiates between covalently bonded molecules and ionic compounds. The electromagnetic forces bit is far too general - start specific and then expand. Vsmith 18:14, 17 September 2006 (UTC)
Also, I provided a definition based on a widely used text reference. A modification of that definition to not be supported by the reference is problematic. Our function here is not to define based on our background in biochemistry or whatever, or our original research, but to report existing info. A basic definition following an introductory level text, followed by expansion/clarification for other usages is preferred. Vsmith 18:24, 17 September 2006 (UTC)
"Existing info" includes how working biochemists use the term. So it needs to be included in the definition. There is no such thing as a "basic" definition when it comes to something like molecules. This is due to the fact that most people working with molecules are somewhat sophisticated, don't you know. The basic bonding in SOME molecules is entirely covalent, and in others it's not. If you have a crystal of human hemoglobin, the hemoglobin "molecules" in it are composed of protein tetramers, which are held together with hydrogen bonds. Worse still, these tetramers in the crystal are held to each other with hydrogen bonds, too-- just not quite so strong ones. Basically, a "molecule" is a chemically-defined repeating unit which you find in a covalent solid or liquid, which "explains" the chemistry of the stuff, without having to go to larger structures. For non-covalent materials like metals or ionic solids, all bets are off and we don't speak of molecules. For network covalent solids like graphite or diamond all bets are off and we don't speak of molecules. For gases, it's easy: "molecules" are the gas particles bouncing around and separated by large empty spaces of vacuum, no matter what their structure. SBHarris 18:31, 17 September 2006 (UTC)

Vsmith, you are very inflexible and you argue in a way that contradicts yourself. Specifically, I was the one who originally provided a definition based on a widely used text reference (see: April 24, 2006 edit):

In chemistry, a molecule is an aggregate of at least two atoms in a definite arrangement held together by special forces. (Chang, Chemistry 6th Ed.)

It was you who modified that definition so to make the situation problematic. You state that your widely used 4th edition text supposedly replaced my 6th edition text. Sounds backward to me? --Sadi Carnot 16:03, 18 September 2006 (UTC)

Moreover, here are more “textbook” definitions:

Molecule – a definite group of atoms that are chemically bonded together, i.e. tightly connected by attractive forces. (Ebbing, General Chemistry, 3rd Ed.)
Molecule – a chemical combination of two or more atoms. (Brown, LeMay, Bursten, Chemistry – the Central Science, 9th Ed.)
Molecule – a group of atoms bonded to one another. (Pauling, General Chemistry, 3rd Ed.)

I hope these definitions clarify my point; I will now change the definition accordingly per these defintions and the above vote. --Sadi Carnot 16:33, 18 September 2006 (UTC)

Where is this vote? This is a supposed discussion, not a vote. Inflexible? Simply said start simple and then expand the definition to cover variables introduced by biomolecules, polymers and supermolecules. Covalent bonds are the most prevalent bonds within molecules - especially simple species such as water, methane, ammonia, etc. The additional text defs provided do indicate a lack of rigor among text writers - the definitions are quite vague and could include almost anything. And that held together by special forces bit makes it sound like a military thing -- leastwise that's the image that special forces pops into my head. Cheers, Vsmith 00:32, 19 September 2006 (UTC)

Okay, I vote 'for' :-) Everyone is right and the views expressed above actually complement each other. I personally tend to favor this current version of the introduction:
molecule - an aggregate of two or more atoms in a definite arrangement held together by chemical bonds.
as a very balanced one. I guess it is as difficult to define a molecule as it is to define a planet, and scientists' subjectivism and conflicting egos will always complicate matters, no doubt. --Unconcerned 03:04, 19 September 2006 (UTC)
Yes, I concur (vote) with Unconcerned and SBharris. This definition is all inclusive. Moreover, both the Oxford Dictionary of Chemistry and the Barnes & Noble Essential Dictionary of Science state that a molecule can be a group of atoms held by either covalent, ionic, or coordinate bonds, thus "chemical bond" is the generic label for all of these types of bonds as well as all others, such as "hydrogen bonding", "non-covalent bonding", etc., I hope this wraps this discussion up. Thanks: --Sadi Carnot 17:58, 19 September 2006 (UTC)

So, is sodium chloride composed of molecules? How about silica or diamond? Or graphite? And how about a protein, DNA? How about acetic acid dimers in gas phase? If you ask me, the answers would be no, no, no, no, yes, two different, two identical. Chemical bonds seem a bit loose for a definition. Does it include ionic bonds? --Rifleman 82 11:54, 6 November 2006 (UTC)

Sodium chloride is a molecule in the gas phase, but not in the solid. I think the key is that a molecule needs to be "discrete" as opposed to "infinite", but the distinction is sometimes blurry. - Itub 17:43, 6 November 2006 (UTC)
Concur with Itub. --Sadi Carnot 08:05, 26 January 2007 (UTC)

Encyclopedia Britannica defines a molecule as: "the smallest identifiable unit into which a pure substance can be divided and still retain the composition and chemical properties of that substance." The definition paragraph says this breaks down but offers no citation. Reading this discussion I see that various chemistry encyclopedia's offer different definitions but none seem to refute the Britannica definition. We should keep in mind that wikipedia should be accessible to the largest audience possible and not just to specialists. Please review the copy of the Encyclopedia Britannica article at:

[2]

If there is no comment regarding my discussion post within a reasonable amount of time I will be inclined to change the first paragraph to match the Britannica definition.

sabbetius 19:37, 27 May 2007 (UTC)Sabbetius

There are problems with Britannica's definition since "rocks, salts, and metals, are composed of atoms or ions, but are not made of molecules." I think that the Encyclopedia Britannica's definition is reflected in the intro paragraph. In fact I think the first paragraph is a pretty good since it reveals the fact there are many different definitions. I would be opposed to changing the paragraph to more closely match Britannica. M stone 22:25, 27 May 2007 (UTC)
Which compounds are not composed of molecules? Wouldn't rocks and metals just be formed by more complicated molecules that would require less effort to break apart, and thus lose their essential properties? I still do not understand why the Britannica definition is not applicable.sabbetius 02:47, 28 May 2007 (UTC)
I move to revert to the EB definition, or at the very least mention it prominently in the intro paragraph. No conclusive argument has been offered on why we should disregard it. The definition of a "molecule" is a stipulative definition: how can there be problems with a stipulative definition (unless, of course, it's either too vague, or it doesn't outline the boundaries of any class of instances whatsoever (note that none of these are faults of the EB definition))? You may argue that the definition is not useful or something similar, but certainly not that it "breaks down" in some unspecified manner. Aqualung (talk) 20:12, 17 October 2010 (UTC)

History of the molecule[edit]

Moved to: Talk:History of the molecule

Definition of molecules does not require bonds![edit]

Despite the fact that the overwhelmingly vast majority of molecules are composed of greater than one atom this is not a requirement! The definition of a molecule is the smallest component of a pure compound that retains all properties of the compound. This is a practical definition. A pure compound is composed of only one kind of molecule. This is what scientists understood before they understood the concept that bonding. Of course noble gases are molecules despite the fact that the are monoatomic! If you use this definition then the questions that are being posed can be answered by the definition instead of intuition. If you don't believe me then try to stump me. M stone 00:38, 1 May 2007 (UTC)

Wikipedia does not publish your original thoughts - please provide references to reliable sources. Cacycle 01:19, 1 May 2007 (UTC)
  • Common knowlege does not equal orginal research. M stone 07:04, 1 May 2007 (UTC)
We did allow for monatomic molecules (one atom, no bonds) in the LEAD paragraph, though we didn't qualify the first sentence to allow for the qualifying sentence which would come right after (I think we should have). But simply defining molecules as the smallest unit which retains all the properties, or even all the chemical properties of the bulk compound, is not really an easy way out, either. The reason is that really small aggregates of atoms (of an element, for example) can have quite different properties than the same atoms taken singly or in bulk. Surface tension and wetness and viscosity are obvious physical properties which depend on sheer numbers. But even chemistry depends to a shocking extent on surface properties, and nanoparticles of network solids will have different properties the further you want to subdivide them. Metals in colloidal dispersions are famous for catalytic properties not seen in other forms. You may argue that this only means they never have molecules in the usual sense. But it's much easier to define a "molecule" as that common aggregate which you often seen flying through the vacuum, in a MALDI-TOF mass spectrometer.SBHarris 02:15, 1 May 2007 (UTC)
  • I think that the purity qualification addresses some of the points you have made. In other word if define the compound as being pure then you are implying that it is only composed of one type of component. However, you are correct that some properties do not scale. Thus I propose a revision that The definition of a molecule is the smallest component of a pure compound that retains all inherent properties of the compound. M stone 07:04, 1 May 2007 (UTC)

My opinion is that the most sensible definition of molecule should include monatomic entities such as noble gases. Unfortunately, all the commonly accepted definitions, including IUPAC's, require that molecules have at least two atoms. So that's what we must report in Wikipedia. --Itub 20:13, 6 May 2007 (UTC)

  • I am reversing my earlier statement after checking around further it does seem that most definitions of molecules require at least one covalent bond. I think as it stands the current definition is good. Older definitions do seem to have some drawbacks. M stone 21:45, 11 May 2007 (UTC)

edits to definition and introductory section[edit]

Cacycle, you have just reverted the introductory section of that article to a vulnerable state that in the past had justified a long series of wild edits and contributions. The version you have modified was the result of a cooperative effort of capturing the essence of various definitions and aspects, and --rather than being stale-- it was relatively stable for a long period of time because of the achieved consensus. Please take a look at the history and the discussion page.

I was aware of that discussion and decided to be bold. There is no reason to keep a bad version just because it is "stable". Cacycle 03:33, 1 May 2007 (UTC)

The IUPAC definition by itself is not sufficient for the broader scope of this article as it is given from the narrow perspective of theoretical chemistry. The multiple citations referenced by user:Sadi_Carnot as note 1 are proof of the wide inconsistence in defining a molecule among authoritative academia circles.

My rewrite did not change this (beside the uncharged part which we might move somewhere else):
In science, a molecule is a sufficiently stable electrically neutral group of at least two atoms in a definite arrangement held together by strong chemical bondss. Only in the kinetic theory of gaseses the term molecule is often used for any gaseous particle regardless of their composition.
Cacycle 03:33, 1 May 2007 (UTC)

Also, the short discussion about divisibility that you have wiped was provided in support of that most general definition involving the "smallest particle..." and is of historical importance (see for ex. here as well as history of the molecule)

It is not wiped, it is still there in the intro. I have just removed some unnecessary redundant introduction:
Molecules and atoms are the smallest particles of pure chemical substances that still retain their composition and chemical properties.
Cacycle 03:33, 1 May 2007 (UTC)

Also, it is incorrect to include NaCl in the discussion about network solids. That discussion was intended to differentiate the concepts of covalent vs. molecular.

If you read it again you will see that sodium chloride is an example of a salt, not of a network solid.
No typical molecule can be defined for ionic (salts) and covalent crystals (network solids) which are composed of repeating unit cells that extend either in a plane (such as in graphite) or three-dimensionally (such as in diamond or sodium chloride).
Cacycle 03:33, 1 May 2007 (UTC)

I guess the general message here is that most things were included in the article for a reason, and hope you will reconsider your next edit, but for now I am revering to the mentioned version and would appreciate your discussing the intended contribution on the talk page--Unconcerned 03:10, 1 May 2007 (UTC)

I was very well aware of the above discussion and I decided to be bold and to remove the clutter and to correct were needed. Please see my remarks above in your posting. I still stand to my edits and hope that we can reinstate my recent edits soon. Cacycle 03:33, 1 May 2007 (UTC)
My nitpicking version changes and tracking my own contributions didn't help with staying objective. I actually like how it reads overall and apologize for not making the extra effort to read the whole intro and overview before dismissing everything. I only hope it will resist "innovative" rewrites as it has seen in the past (or reverts from superficial users like myself for that matter.)--Unconcerned 05:52, 1 May 2007 (UTC)
Thanks :-) I have updated the intro about the uncharged requirement. Feel free to edit this version for a better style (e.g. the sodium chloride sentence). Cacycle 13:11, 1 May 2007 (UTC)


The smallest molecular species?[edit]

I think that the statement "The smallest molecular species that has a bond is the hydrogen ion molecule H2+, comprised of two protons bonded together by the sharing of one electron" is incorrect. I would assume that removing an electron would increase the bond length and thus H2+ would be larger in size than to nuetral H2. H2+ is the molecule with the least number of total electrons, however I am not sure why this is important. I think that this statement needs to be corrected or referenced. M stone 06:06, 25 May 2007 (UTC)

I put that there, because it is a very notable fact, according to Linus Pauling, from his The Nature of the Chemical Bond (the book known as the "bible of modern chemistry"), ch. 1, where he states that "the simplist of all the molecules is the hydrogen molecule-ion, H2+", and the "simplist of all the chemical bonds is the one-electron bond. If you want to understand the quantum mechanical nature of chemistry, according to Pauling, this is the place to start. Thats why its important. --Sadi Carnot 18:56, 27 September 2007 (UTC)
H2+ is important in theoretical chemistry because it is the "smallest" molecule in terms of numbers of particles. The Schrodinger equation for it can be solved without having to worry about electron-electron repulsion. Of course, all of this is not especially relevant for a section about molecular size, where the statement that you removed used to be. More than "smallest", I would say "simplest". Whether H2+ belongs in this article at all is not too clear to me, but I think that it would deserve mention if we had a short section about "quantum theory of molecules". --Itub 15:26, 6 June 2007 (UTC)
I agree that H2+ is relevant as the "simplest" molecule. M stone 20:15, 6 June 2007 (UTC)
I should add that H2+ is not even a molecule by the lead definition in the article, because it is not electrically neutral! ;-) However, theoretical chemists often call it a molecule. It all depends on the context. --Itub 09:09, 8 June 2007 (UTC)

Something needs to be added to define molecular species, particularly molecular ions such as H2+ and common ions like sulfate. I'm not sure where though. Any ideas? --Bduke 09:18, 8 June 2007 (UTC)

Probably in a new section. The sections are pretty independent so the order is not obvious. Perhaps after the overview? --Itub 10:51, 8 June 2007 (UTC)
It seems like someone has removed the "smallest molecule" tidbit from the article; I will re-add it per Linus Pauling's ref. --Sadi Carnot 12:13, 28 September 2007 (UTC)
It was never removed, I moved it to the Theoretical aspects section. Now that you added it back, there is a large amount of needlessly redundant repetition. ;-) --Itub 13:44, 1 October 2007 (UTC)

Size images (in angstroms)[edit]

I didn't see that bottom part. In any event, I cut a sentence out, it seems ok now. Also, I think we should get some images in the "molecular size" header section, so that people can get a feel for what an "angstrom" is. Later: --Sadi Carnot 18:34, 1 October 2007 (UTC)

I thought that consensus was reached on H2+. It is confusing to talk about size in terms of the number of particles. H2 is the smallest molecule because it has the shortest bond length. H2+ is the simplest molecule because it is composed of the fewest number of particles. However, H2+ is larger than H2. I have changed things back to previous consensus. would appriciate if a bond length were found for H2+ before it was readded. M stone 19:35, 1 October 2007 (UTC)

I agree with Stone. BTW, the bond length in H2+ is 1.06 Å.[3] --Itub 04:41, 2 October 2007 (UTC)

Merge Molecular compound here[edit]

I'm not sure I understand what Molecular compound is trying to say. I think it is meaning molecules and so anything new should be here. It apparently is to contrast with Ionic compound; but, I don't believe molecular compound is a common usage. ChemGardener 02:54, 22 June 2007 (UTC)

Now a redirect, the content had many errors. Cacycle 04:00, 22 June 2007 (UTC)

Human molecule?[edit]

Moved to Talk:Human molecule. --Sadi Carnot 14:30, 28 September 2007 (UTC)

Small molecule redirect[edit]

In Molecular biology the "small molecule" name applies to organic molecule that are not biopolymers and that are not biologically inert (they are small as a consequence of not being a polymer). it redirects here, which is not good. So I will make an article and see what I can conjure up. Help very welcome. --Squidonius (talk) 23:47, 5 May 2008 (UTC)

Question, Atoms/Element[edit]

I know a few elements that combine with others to form a molecule, like:

  • Hydrogen - 1 bond
  • Oxygen - 2
  • Nitrogen - 3
  • Carbon - 4

What other atoms/elements are there? Please awnser Androo123 (talk) 19:45, 20 June 2008 (UTC)


External links are all spam[edit]

I think that external links are all spam. I just noticed based on the most recent addition. I think they should all be erased. M stone (talk) 10:56, 28 June 2008 (UTC)

I do not think that "molecule of the month" is spam. This is an interesting site that is recognized by chemistry web pages across the world and has been for 10 years or so. It almost is notable enough for an article. I have no comment on the others. --Bduke (talk) 12:13, 28 June 2008 (UTC)
I think that it would be more appropriate to make a "Molecule of the month" article and list under "See also". I will delete the rest and leave it up to you. M stone (talk) 05:16, 29 June 2008 (UTC)


Definition[edit]

"... a molecule is defined as a sufficiently stable, electrically neutral group..."

"The simplest of molecules is the hydrogen molecule-ion, H2+ ..."

P99am (talk) 09:30, 24 April 2009 (UTC)

Does seem rather out of place as it is a polyatomic ion ... but it is used in the theoretical section as "the example" for the Schrödinger equation "easy solution". Not sure that it really needs to be here without further clarification as it is not a "simple molecule" and not neutral - just adds confusion as is. Vsmith (talk) 12:34, 24 April 2009 (UTC)

I think that the main problem is not in the hydrogen ion, but in the definition. It may be better to say:

  • Believe ...
  • Molecules are called ...
  • Typically, a molecule considered as ...

Not "is defined".--P99am (talk) 12:57, 24 April 2009 (UTC)

I disagree. Definitions should place clear boundaries because they are meant to delineate simple concepts rather than objective truth. Science has repeatedly shown that physical reality branches into layers of ever increasing complexity. What we typically do is come up with additional sets of clearly defined concepts rather than tweak and redefine existing ones. Thus, the molecule definition will never be capable of describing everything scientists call molecule these days without losing clarity and usability. The definition has historically branched from simply molecule to monatomic and polyatomic molecule to the quantum chemical concept of everything in a potential well is a molecule, when, in fact, the simplest, original definition will always give the clearest picture of what this concept is all about: smallest particle of a substance still preserving its chemical properties. Just my $0.02. --Unconcerned (talk) 14:24, 29 April 2009 (UTC)

Your definition is much better than given in this article. Nevertheless, it does not make clarity. And no one definition of the molecule create clarity. And it's good. We need explanations, not definitions.--P99am (talk) 15:24, 29 April 2009 (UTC)

Of course we need both definitions and explanations. They're not mutually exclusive. Just FYI, Wikipedia has a very good summary of what very smart people think a good definition is. Definitions provide the skeleton, the structural framework for solid knowledge. I don't see how one can build a good explanation of a concept without a crisp, solid definition at its foundation. Just another 2 cents' worth. Keep it goin' and soon there'll be enough cents to buy a beer ;-) --Unconcerned (talk) 18:18, 29 April 2009 (UTC)

molecules —Preceding unsigned comment added by 75.74.111.30 (talk) 21:51, 26 August 2009 (UTC)

image[edit]

Can this image be added to this article? That is the best image of a molecule in existence. 85.65.69.166 (talk) 03:15, 1 September 2009 (UTC)

Sure, why not? SBHarris 05:20, 26 February 2010 (UTC)
Because it is a fair use image, which is copyrighted by a flickr user (probably IBM employee). It may not be used for more than one article on wikipedia - in this case, pentacene - as the only available image illustrating the object of the article. Materialscientist (talk) 05:37, 26 February 2010 (UTC)

image show now ¢$₯₣ — Preceding unsigned comment added by 39.32.88.30 (talk) 17:57, 22 October 2013 (UTC)

Please add some Photos of molecules from real life[edit]

i believe that an article about molecules should show at least 3-5 photos of molecules from microscopes... — Preceding unsigned comment added by 79.182.15.64 (talk) 10:39, 19 September 2011 (UTC)

The first image of the page[edit]

that
The text under this image is faulty. It states that the middle and left images are 3d, and that the right one is 2d. The problem is that the right one also is (partially) 3d. As you guys know the way the bonds are displayed gives information about the invisible z-axis. It's not very obvious and more of a wrong nuance, but I do think something should be changed.
Potential solutions are, change the text and change the image.
The information given by the text is valid and relevant, so I think it is preferable to change the image.
What do you guys think?
Bartiosos (talk) 08:25, 12 February 2014 (UTC)