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a Bronsted Lowry Acid is defined as an acid that donates a proton. However it's actually a Hydrogen Ion, since hydrogen only has 1 proton and 1 electron, a positive Hydrogen Ion would have no electron and therefor only be a proton which is why we call it that. However Isotopes exist: deuterium has 1 neutron and tritium has 2, my question is: Can an (Bronsted Lowry) acid donate a hydrogen Isotope? Is the naming just out of convenience or very specific? Surely an acid can donate a deuterium ion, or perhaps there's a reason these isotypes are different?

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  • $\begingroup$ Deuterium works essentially the similar way as hydrogen but only slower. For example, in benzyne mechanism, the reaction slows down if hydrogen is replaced with deuterium showing isotope effect. $\endgroup$ Jun 4, 2023 at 10:51
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    $\begingroup$ BL theory have been created 8 years before deuterium discovery. It was left as is probably for simplicity as D relative abundance is about 0.015%. Whoever works with deuterated acids is aware of this formulation inaccuracy. $\endgroup$
    – Poutnik
    Jun 4, 2023 at 11:13
  • $\begingroup$ Note that some formulations say "hydrogen cation". $\endgroup$
    – Poutnik
    Jun 5, 2023 at 9:37

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Just remember that titles and names do not matter for elements or atoms. As Shakespeare wrote "What's in a name? That which we call a rose, by any other word would smell as sweet." An element is to be identified by the number of protons ($Z$) not by the number of neutrons or electrons. Isotopes have very similar chemical properties, but their reaction rates are different because of different bond strengths. Say, you have HCl gas (dissolved in $\ce{H2O}$) and DCl gas (dissolved in $\ce{H2O}$), both liquids will still behave like very strong Bronsted-Lowry acids. If you were to add a base like NaOH and NaOD, in each case, one will get water ($\ce{H2O}$ and $\ce{D2O}$) and salt as products. Heavy water is still chemically "water".

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In its common usage "water" is not definitive. A quick glance thru the Wikipedia tome on water [read it, the entry on deuterium depleted water, and on Heavy water] affords an amazing array of properties, etc., of H2O with no mention of isotopic [or isomeric, yes H2O has "isomers"] composition. I do not know if the data presented are for isotopically pure H2O or the natural isotopic distribution. Since natural water is mostly H2O its properties are very similar to but not identical to pure H2O. Natural water also differs depending on the source; there is more D in the oceans than in water vapor, fresh water, or glacial ice [I do not know about sea ice].

Natural water devoid of non-water impurities is a mix of many compounds: H2O, HDO, D2O, H2O[17] and its D analogues. H2O[18]and its D analogues culminating in the super heavy D2O[18]; there is also the mix of ortho and para-H2O and the trace of tritium compounds. We are fortunate that this can all be almost ignored and left to the specialists to worry about.

These, excepting the HD and o,p compounds that can interconvert, are distinct chemicals with distinct, while similar, chemical and physical properties. The differences manifest in kinetic isotope effects and in the compositions of products in reactions that do not reach equilibrium or completion. D2O is a slightly weaker acid or base than H2O. Mixes act as mixtures.

Isotopes are similar chemically but can be very different in nuclear and spectroscopic properties. Low temperature behavior of Helium[3] and Helium[4] is an example; They are almost different elements.

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  • $\begingroup$ What is the reason for the downvote? $\endgroup$
    – jimchmst
    Jun 7, 2023 at 3:14

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