Can H+ ion exist independently since it does need to form any bonds.Why do we say that it needs to be in H30+ ion form?

  • 2
    $\begingroup$ Please explain. What is the meaning of "independently" ? Independently from what ? Or do you want to know whether H+ exists alone, without any water arounds it ? In the vacuum of a mas spectrometer, the ion $\ce{H^+}$ does exist. Not in water. $\endgroup$ – Maurice Oct 20 '20 at 10:29
  • $\begingroup$ Yes I want to know whether H+ ion can exist alone. $\endgroup$ – srijan Sri Oct 20 '20 at 10:49
  • $\begingroup$ As long as there is something (partially) negative around, a proton will be drawn to it. In aqueous solution it forms (in first approximation) $\ce{H3O+}$. $\endgroup$ – Martin - マーチン Oct 20 '20 at 10:52

Be aware that $\ce{H+}$ is nothing else then a proton $^1_1\mathrm{p}$. Protons have an extreme charge density, typically $10^{15}$ higher than any other ion ( but bare electrons or atomic nuclei).

Protons can exist free in vacuum or plasma, but even in gases they quickly react with many gaseous molecules, forming molecular ions, like dioxidanylium $\ce{O2 + p -> HO2+}$.

Protons act in aquaeous environment as extremely strong Lewis acid with an electron pair of $\ce{H2O}$(Lewis base), forming a ion called hydronium, a particular type of oxonium ions.:

$$\ce{p + H2O -> H3O+(aq)}$$

For convenience, we often use notation $\ce{H+}$ or $\ce{H+(aq)}$, supposing it is at least $\ce{H3O+(aq)}$.

Experiments mentioned in the above Wikipedia link confirm hydronium is usually coordinated with 6 water molecules as $\ce{[(H3O)(H2O)6]+}$, but multiple various hydration structures have been observed or assumed, like
Zundel ion $\ce{H5O2+}$,
$\ce{H9O4+}$($\ce{H3O+ . 3H2O}$)
or a cluster $\ce{H3O+ . 20 H2O}$

Note that the hydronium ion forms solid salts with acids with dissociation constant $K_\mathrm{a} \gt 10^{9}$.
E.g. a crystallic monohydrate of perchloric acid is hydronium perchlorate $\ce{[H3O+][ClO4-]}$


If we try to answer this question at a rather simple level, we could say that yes the ions can exist in a particle-free environment like vacuum. But if ions are formed in an aqueous medium, like the H+ ions in acidified water then the H+ readily combines with H2O to form hydronium ion. Which means that the H+ is not stable but since it can't combine with anything in vacuum, it exists. But as soon as there's something it could combine with, it'll readily do so. That is the reason they say we must mention it to be in hydronium ion form when it is formed in an aqueous medium.


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