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Aakash Pandita

When water can form an H30+ ion why can't it form an H4O2+ ion?

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Is it that protons tend to join other H2O molecules rather than forming H402+?

 

It would have to form a double bond, that is a clue.

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It would have to form a double bond, that is a clue.

 

no it wouldn't.

 

Anyway, the H4O2+ ion is less stable than the H3O+ ion.

 

you could concievably get it to form but it would require an abundance of H3O+ ions likely, nothing but. but to keep the thing electrically neutral you'll need negative ions. basically, it'll decompose to a whole lot of water first.

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OK, why would a positively charged H3O+ ion stick to a positively charged H+ ion that is repelled by the laws of electrostatics?

H4O++ isn't going to exist because it would fall apart to H3O+ and H+

 

If you got bored you could work out roughly how much energy would be released by the decomposition of the hypothetical molecule and then work out the equilibrium constant for the reaction.

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OK, why would a positively charged H3O+ ion stick to a positively charged H+ ion that is repelled by the laws of electrostatics?

H4O++ isn't going to exist because it would fall apart to H3O+ and H+

 

If you got bored you could work out roughly how much energy would be released by the decomposition of the hypothetical molecule and then work out the equilibrium constant for the reaction.

 

That and there just aren't any p-orbitals left on the oxygen atom.

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I had a quick Google search on H4O2+, and I guess nobody has tried to measure it yet.

Neutral H2O has 2 lone pairs, which could theoretically both form a bond with a proton to give the H4O2+ ion. So, from a structural point of view, there is no problem. But as John Cuthber suggests, even if this reaction is theoretically possible, the equilibrium might be so far in the direction of the H3O+ (and also H2O), that there is not a single H4O2+ in all the world's oceans. But the question is not

 

As some other people online suggest however (and summarized in my own words): There is probably also no such thing as H3O+. Instead, it's a proton which is stabilized by a whole bunch of water molecules. Some people prefer to write it as H+. Some say H3O+. And some say it should be something like H3O(H2O)4+, or H3O(H2O)9+ or so. Water will form a hydrate around anything that has a charge in liquid water. And those hydrates stabilize ions, and make it possible for ions to physically separate themselves from the ions with the opposite charge.

 

A simplified model that does not take into account large structures of hydrates would therefore not be able to predict such a H4O2+ ion. And, therefore, I don't think that John Cuthber's suggestion to calculate the decomposition energy is very straightforward. The decomposition of NaCl into Na+ and Cl- is also massively unfavorable when it's considered as such. But as soon as the hydrates of water enter the picture, this reaction proceeds rapidly.

 

I don't think there is enough information to dismiss the existance of H4O(2+) altogether.

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I had a quick Google search on H4O2+, and I guess nobody has tried to measure it yet.

Neutral H2O has 2 lone pairs, which could theoretically both form a bond with a proton to give the H4O2+ ion. So, from a structural point of view, there is no problem. But as John Cuthber suggests, even if this reaction is theoretically possible, the equilibrium might be so far in the direction of the H3O+ (and also H2O), that there is not a single H4O2+ in all the world's oceans. But the question is not

 

As some other people online suggest however (and summarized in my own words): There is probably also no such thing as H3O+. Instead, it's a proton which is stabilized by a whole bunch of water molecules. Some people prefer to write it as H+. Some say H3O+. And some say it should be something like H3O(H2O)4+, or H3O(H2O)9+ or so. Water will form a hydrate around anything that has a charge in liquid water. And those hydrates stabilize ions, and make it possible for ions to physically separate themselves from the ions with the opposite charge.

 

A simplified model that does not take into account large structures of hydrates would therefore not be able to predict such a H4O2+ ion. And, therefore, I don't think that John Cuthber's suggestion to calculate the decomposition energy is very straightforward. The decomposition of NaCl into Na+ and Cl- is also massively unfavorable when it's considered as such. But as soon as the hydrates of water enter the picture, this reaction proceeds rapidly.

 

I don't think there is enough information to dismiss the existance of H4O(2+) altogether.

You don't?

Which part of "like charges repel" is giving you trouble?

And, while I accept that a calculation wouldn't be very precise. it would show that the molecule simply wouldn't exist.

(I can state this with no fear of being proven experimentally wrong)

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You don't?

Which part of "like charges repel" is giving you trouble?

And, while I accept that a calculation wouldn't be very precise. it would show that the molecule simply wouldn't exist.

(I can state this with no fear of being proven experimentally wrong)

Your post is a fallacy. Essentially, you use a form of a non sequitur: your conclusion does not follow from your premises. You throw in some rhetorical questions that I'd like to see answered (i.e. they're not rhetorical), and you even open the post with a (albeit modest and polite) personal attack. "You don't?" sounds a little like I'm the silly one who does not seem to get it. Well, let's assume that "I don't". You state that there seems to be no experimental evidence that this structure exists, but that in itself is not enough proof to conclude that it indeed does not exist.

 

If you would merely be saying that I (or anyone else in this thread) does not present enough evidence to conclude that it DOES exist, I would agree. We don't present enough evidence, and such a conclusion would be wrong. But you take this a step further, and you conclude that it does NOT exist. And such a conclusion requires its own evidence, which you present in the form of a calculation which you don't want to do. That's not enough.

 

"Like charges repel" gives me no trouble, but larger charges than +2 exist in nature on a single atom. Nature seems to have no problem with that. Also, in a theoretical H4O2+ structure, oxygen would still be in its favored 2- oxidation state. Now, don't get me wrong, I know that there are a LOT of reasons why this structure is unlikely. And I certainly don't claim that the laws of acids and bases are not valid. I am aware how equilibria work. But I am not yet convinced that it's completely impossible under all circumstances that this structure never exists.

 

If this would be an equilibrium reaction, for example:

2 H3O+ <<<--> H2O + H4O2+

Or perhaps:

3 H2O <<<--> 2 OH- + H4O2+

 

Then the equilibrium would lie completely on the left, meaning that for all practical purposes we might as well assume that the concentration is zero. But as far as I'm concerned, we are not talking only about practical cases here. I want to know whether somewhere in our oceans, this H4O2+ could exist, if only for a moment.

 

There are people who calculated the wave function of the H4O2+ ion (note: .pdf, scientific article), and although I do not claim to actually understand the physics behind that, I do not read that its existance goes against the laws of physics.

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I doubt it would exist in the ocean, but:

 

http://www.sciencedirect.com/science/article/pii/0009261487804906

 

Also, Captain

 

"Like charges repel" gives me no trouble, but larger charges than +2 exist in nature on a single atom. Nature seems to have no problem with that. Also, in a theoretical H4O2+ structure, oxygen would still be in its favored 2- oxidation state.

 

You've argued a strawman here. Plenty of atoms exist with formal charges > +1, but this is not (I think) what John was arguing. He seemed to be more pointing out the fact that the reaction between two cationic species is not going to happen readily because the charges repel, which is true.

 

That being said, there was this:

 

The formation of a divalent species like H4O2+ shown in Figure 1(a), would be normally energetically not favored in water because two positive charges are being pushed together on the same water molecule. But in the above case the water molecules act as a carrier of two hydrogen ions with the help of two independent dative bonds formed between the two lone pair electrons in the oxygen and the two hydrogen ions.

 

Which comes from this PDF article.

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On the main topic

First of all, hypervalent_iodine, thanks for those links. I think that gives the answer to the question in this thread, which I propose to summarize as follows:

 

Is it that protons tend to join other H2O molecules rather than forming H402+

Answer: in ordinary water, there is no indication that this ever happens. In specific systems, the H4O2+ exists, as shown in the links provided by hypervalent_iodine. If the H4O2+ exists at all in ordinary water, then it exists in such low concentrations that we have not yet measured it.

 

Bickering over details

When some of you said "it does not happen", or something similar, I take that as the mathematical form of zero. Literally never.

But I think you mean to say: "it is extremely unlikely and in every practical sense can be ignored", which is mathematically like a very very small number but not zero.

 

In this case, I think it is important to distinguish between the two. I am not sure I was on the same line as the rest of you though.

 

You've argued a strawman here. Plenty of atoms exist with formal charges > +1, but this is not (I think) what John was arguing. He seemed to be more pointing out the fact that the reaction between two cationic species is not going to happen readily because the charges repel, which is true.

Hmm... agreed that I seem to miss the point a bit in my explanation. I did not intend to argue a strawman there, I meant to indicate that if you have any atom with a formal charge of +2 or more, and when this goes into solution, you obtain a stabilized structure (stabilized by hydrates) which has a charge of more than +1. Either a redox reaction or an acid base reaction (self-ionization of water) could compensate that, but that this does not happen, because that would be energetically unfavorable. (*)

 

Also, I believe in certain cases same charges do not repel. For example, a Hg+ ion in solution bonds with another Hg+ ion to form Hg22+, indicating that it's not completely impossible to have interactions between ions of the same charge, as long as a more energetically favorable component is made. I am not entirely sure if I got the mechanism correct here, and I agree it's not really comparable to the proposed system of water.

 

Anyway, thanks again for the links. I wasn't able to find them myself. It shows to me that the H4O2+ does indeed exist, but so far it has only been detected in specific systems, and I think only as an intermediate.

 

(*) Actually, that's also an equilibrium, and it does happen, but not much.

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2 hours ago, DEEP chowdhury said:

But in bonding of h3o a lone pair is left can there a H+ ion can't go. Pleseeeeee give me my reply

 

Could you please be a little clearer with what you're asking?

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Go to this website and you will find that research has been done on it already and H4o++ ions may actually exist :-

https://www.researchgate.net/publication/236979363_On_the_existence_of_the_protonated_hydronium_dication_H4O_in_sulfolane_solution

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