[Aymeric]

Hello,

This is a very basic question which probably reflects a lack of understanding of some fundamental concept, but I can’t tell what.
I’m wondering why electrons are referred to as e- while protons are referred to as H+. Since H is exactly one proton and one electron, why have protons been associated with H while electrons get their own atom-independent notation?
This tends to complicate things for me. For example when we talk about NH3+, why not just write it NH2+ (which would be N with two covalent H, and an extra proton represented by the +, just like COO- is a C with two covalent O and an extra electron noted -).
The actual notation system as I understand it blurs things because I always have to go like ’ok NH3+, so there are 3H, no wait just 2 because the 3rd one is only half an H because it has an electron missing’. It’s rather convoluted.

Obviously I already know that things are the way they are for a very good reason and the problem lies within my own understanding which is flawed somewhere. I’d be grateful to anyone who could tell me exactly where I misunderstand the system.

Thanks!

[Aymeric]

Re-reading myself I think I’ve made a complete mess of the issue, but I can’t delete the thread so please don’t bother replying until I’ve gone over the issue with a clearer mind! Thanks...

[Babcock_Hall]

I might be able help a little.  An H atom, symbolized as H•, is a proton and an electron, and it has no charge.  H⁺ is just the proton without an electron. The signs "+" and "-" reflect charges.

[Borek]

You can split hydrogen atom into an electron e^- and a proton p⁺. p⁺ and H⁺ are synonyms, just used in different contexts - p⁺ is common in nuclear physics, H⁺ is common in chemistry.

Typically when we talk about chemical properties we use H⁺ notation, when we deal with nuclear reactions and high energies where chemical properties don't matter, we use p⁺ notation.

[Aymeric]

Thank you both for your answers. I don’t want to sound too fussy but is there any straightforward explanation as to why H+ is a more suitable notation than p+ in chemistry?
Coming back to the example I used with NH3+ and COO-, wouldn’t the most intuitive way to write NH3+ actually be NH2+ or NH2p+? Spontaneously NH3+ sounds like there are three hydrogen atoms plus a proton, just like COO- is indeed two oxygen atoms plus an electron...

  H⁺ is just the proton without an electron.

But then why not call electrons H- for the sake of consistency?

What I don’t understand is the logic behind calling a proton a "half hydrogen" instead of simply calling it "proton" and representing it as a proton (p+) instead of representing it as a "half hydrogen" (H+). This would help make the difference between actual hydrogen atoms in a molecule, and the "fake hydrogens" which are actually protons (?).

Thanks!

[Borek]

is there any straightforward explanation as to why H+ is a more suitable notation than p+ in chemistry?

Because in chemistry we deal with atoms (sometimes ionized), not subatomic particles. It happens that proton - which is for physical reasons classified a subatomic particle - is also a nucleus of hydrogen.

wouldn’t the most intuitive way to write NH3+ actually be NH2+ or NH2p+?

No, NH₂⁺ would be a completely different things, in NH₂p⁺ you all hydrogen atoms are identical and equivalent, yet one is marked different.

Spontaneously NH3+ sounds like there are three hydrogen atoms plus a proton

No, it sounds like three hydrogen atoms MISSING an electron, so the overall charge is +1 I fell like that can be the part you are missing, +1 doesn't necessarily mean an added proton, it can as well mean removed electron.

But then why not call electrons H- for the sake of consistency?

H^- is not electron, it is a proton with two electrons or a hydrogen atom with an added single electron (an anion), as present in hydrides  again, an important misunderstanding that can be source of your problem.

What I don’t understand is the logic behind calling a proton a "half hydrogen" instead of simply calling it "proton" and representing it as a proton (p+) instead of representing it as a "half hydrogen" (H+). This would help make the difference between actual hydrogen atoms in a molecule, and the "fake hydrogens" which are actually protons (?).

You are definitely confused here but I am not sure if the confusion comes from problems following the convention or from some deeper misunderstanding of the whole process/situation. Actually what you propose would just make things more difficult. At some point after adding an electron to a molecule containing a "proton" in your notation it would miraculously become a hydrogen. H⁺ is a just a ionized hydrogen atom, and it will become a normal hydrogen after recombining with an electron, no miracles required.

[mjc123]

There is no such thing (in common chemistry) as NH₃⁺; are you trying to compare NH₄⁺ with NH₃?

[Aymeric]

There is no such thing (in common chemistry) as NH₃⁺; are you trying to compare NH₄⁺ with NH₃?

Sorry I should have specified I’m asking myself all these questions in the context of aminoacids being amphoteric. When pH is above PI, the amino group is NH2, but when pH goes down it becomes NH3+.

Spontaneously NH3+ sounds like there are three hydrogen atoms plus a proton

No, it sounds like three hydrogen atoms MISSING an electron, so the overall charge is +1 I fell like that can be the part you are missing, +1 doesn't necessarily mean an added proton, it can as well mean removed electron.

Thank you Borek. I’m indeed confused here because my understanding of aminoacid ionization when pH ≤ PI is that more and more protons become available in the solution as pH goes down, so NH2 picks up one of those protons. You are saying that when NH2 NH³⁺ it ditches an electron, unless I misread you. I can’t correlate [H+] going up with NH2 suddenly missing an electron as opposed to gaining an extra proton.

But then why not call electrons H- for the sake of consistency?

H^- is not electron, it is a proton with two electrons or a hydrogen atom with an added single electron (an anion), as present in hydrides  again, an important misunderstanding that can be source of your problem.

I know it isn’t, but that’s a convention that seems to be disaligned with the fact that COO- is literally a C, two O and an extra electron. WYSIWYG literally. Unlike NH3+ which is not to be read literally as "one N, three H and an extra proton". The indication of protons doesn’t mirror the indication of electrons, that’s what bothers me. I’ll go back and read introductory texts and hopefully they might clear this up for me.

You are definitely confused here but I am not sure if the confusion comes from problems following the convention or from some deeper misunderstanding of the whole process/situation.

I honestly have no idea either...

Actually what you propose would just make things more difficult. At some point after adding an electron to a molecule containing a "proton" in your notation it would miraculously become a hydrogen.

I might be starting to understand my misconception: the charge belongs to the entire group, in which all electrons are pooled together, so when there are more electrons than protons, it’s impossible to ascribe the extra electron to any particular atom within the group. Could this be the source of that whole mess I’ve made?
But then I still don’t get how NH2 becomes NH3+ if it’s not about acquiring an extra proton.

At any rate thank you very much Borek for having the patience to indulge me. It reminds me of when I was an undergrad student and was annoyed by those mature students wasting time asking all sorts of questions because they were too inflexible to accept things as they were presented to them. I’m acting just like them now and I can’t help it!

[Babcock_Hall]

Let me use the amino acid alanine and pI.  The pI is the pH at which an amino acid has no net charge.  However at the pI, alanine exists as a zwitterion.  Both the carboxylate group and the ammonium group are charged:  CH₃CH(NH₃¹⁺CO₂^1-.  If the pH is lowered by some means, then some fraction of the carboxylate group will become protonated.  What happens if the pH is raised?

[Aymeric]

Let me use the amino acid alanine and pI.  The pI is the pH at which an amino acid has no net charge.  However at the pI, alanine exists as a zwitterion.  Both the carboxylate group and the ammonium group are charged:  CH₃CH(NH₃¹⁺CO₂^1-.  If the pH is lowered by some means, then some fraction of the carboxylate group will become protonated.  What happens if the pH is raised?

The opposite? If pH goes back to a higher value than pI then both groups lose a proton (which I intuitively ascribe to [H+] decreasing hence creating some sort of osmosis drawing the protons out of the molecule and into the solution, but I’m aware that’s probably a big stretch), so the carboxylate group which had previously gained a proton and was thus in the COOH form loses it and goes back to its ionized COO- form, while the ammonium which had also gained a proton and was in NH³⁺ form goes back to its neutral NH2 form (?).

[Borek]

Spontaneously NH3+ sounds like there are three hydrogen atoms plus a proton

No, it sounds like three hydrogen atoms MISSING an electron, so the overall charge is +1 I fell like that can be the part you are missing, +1 doesn't necessarily mean an added proton, it can as well mean removed electron.

Thank you Borek. I’m indeed confused here because my understanding of aminoacid ionization when pH ≤ PI is that more and more protons become available in the solution as pH goes down, so NH2 picks up one of those protons. You are saying that when NH2 NH³⁺ it ditches an electron, unless I misread you. I can’t correlate [H+] going up with NH2 suddenly missing an electron as opposed to gaining an extra proton.

Unfortunately examples I make not necessarily fit your confusion, they are designed to explain concepts I guess you are confused about, but if my guess is incorrect they are not helpful :/

I never said going from -NH₂ (I added a "bond" to make it look more like amine group) to -NH₃⁺ means ditching the electron, I said "think as if -NH₃⁺ as if it had three hydrogen atoms minus an electron". Look at indices, your schemes are incomplete and don't conserve atoms/charges. You start with -NH₂. It has two hydrogen atoms and is electrically neutral. You add a proton - which adds both +1 to number of hydrogen atoms an +1 to charge, so you end with -NH₃⁺.

This is in a way equivalent to -NH₂ getting an H atom and then loosing an electron: -NH₂ + H  -NH₃  NH₃⁺ + e^-.

But then why not call electrons H- for the sake of consistency?

H^- is not electron, it is a proton with two electrons or a hydrogen atom with an added single electron (an anion), as present in hydrides  again, an important misunderstanding that can be source of your problem.

I know it isn’t, but that’s a convention that seems to be disaligned with the fact that COO- is literally a C, two O and an extra electron. WYSIWYG literally. Unlike NH3+ which is not to be read literally as "one N, three H and an extra proton". The indication of protons doesn’t mirror the indication of electrons, that’s what bothers me. I’ll go back and read introductory texts and hopefully they might clear this up for me.

Sounds like you thing "negative charge means an extra electron ADDED, positive charge means an extra proton ADDED". It doesn't work this way. You should look at total number of protons and total number of electrons, whichever are in excess give the charge (which is more or less what you said in your post).

But then I still don’t get how NH2 becomes NH3+ if it’s not about acquiring an extra proton.

Well... it is about acquiring an extra proton. See the scheme above - adding a neutral hydrogen atom and then removing an electron is equivalent of adding a proton. And that's actually what happens i nthe solution.


I strongly suggest we leave the pI/pH thing away for now, as it is totally irrelevant to the main problem of proton/electron/charge and will only confuse you further.

[Babcock_Hall]

deleted per Borek's request.

[Borek]

deleted per Borek's request.

Call it a "suggestion"