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 -NH
2 (I added a "bond" to make it look more like amine group) to -NH
3+ means ditching the electron, I said "think as if -NH
3+ 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 -NH
2. 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 -NH
3+.
This is in a way equivalent to -NH
2 getting an H atom and then loosing an electron: -NH
2 + H
-NH
3 NH
3+ + 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.