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I am sure I am asking a very basic question but before coming here, I have made multiple attempts to find an answer elsewhere. Or maybe I am simply asking the wrong question, in some sense. If someone could nudge me in the right direction, I would be infinitely grateful to them. Here is what I am trying to understand:

A hydrogen cation added to a hydroxide ion forms water, which is neutral. A lithium cation added to a hydroxide forms LiOH, which is a strong base completely dissociating in a solution. Now, I understand why LiOH should be more alkaline than H2O. What I cannot understand is why it is so much more alkaline? Intuitively, one might expect a more gradual transition going from H to K. After all, H and Li are neighboring elements from the same group, with the same structure of the electron outer shell. Moreover, H in H2O is locked in a covalent bond whereas Li in LiOH is locked in an ionic bond. Ionic bonds are generally considered to be (much) stronger. Why is it not so in this case?

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    $\begingroup$ Well, hydrogen was sometimes also put over chlorine in the Table. In this context it could be appropriate. $\endgroup$
    – Mithoron
    Commented Mar 12, 2023 at 18:24
  • $\begingroup$ The chemical elements of the same group have similar properties except H , H doesnt have the properties of alkali metals so a H+ added to a OH- (hydroxide anion) doesnt have any reason to be similar to the addition of a alkali metal to a OH-. $\endgroup$
    – Volpina
    Commented Mar 12, 2023 at 18:44
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    $\begingroup$ Notice the ionisation energies of H 1312 kJ/mol , Li 520 kJ/mol, Na 496 kJ/mol ( see en.wikipedia.org/wiki/Molar_ionization_energies_of_the_elements ) $\endgroup$
    – Poutnik
    Commented Mar 12, 2023 at 18:48
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    $\begingroup$ chemistry.stackexchange.com/questions/129008/… $\endgroup$
    – Mithoron
    Commented Mar 12, 2023 at 18:52
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    $\begingroup$ So basically you are asking why H and Li are more different than He and Ne, right? H and He are the only period 1 elements, so there is little you can compare them to otherwise. You can describe hydrogen atoms as having one electron in the outer shell (like other group 1), as having a half-filled outer shell (like carbon and the rest of group 14) or being one electron away from a filled shell (like fluorine and the rest of group 17). Also, hydrogen is considered a non-metal and lithium is a no-doubt-about-it metal. Other groups have non-metals and metals, but with metalloids in between. $\endgroup$
    – Karsten ♦
    Commented Mar 12, 2023 at 22:53

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If I understand your question correctly, it sounds like you are interpreting one of the hydrogens in water as being similar to the alkali metals. In other words, you expect to see a similar change as in LiOH and KOH.

Well the reason you don't is because hydrogen is a non metal. It is significantly more electronegative than the alkali metals.

Therefore, H2O is not really hydrogen hydroxide. It's just water. Also, when water dissociates in water, it forms hydroxide ions but also protons. So, concentration of both is equal and pH is neutral. As a result, water is not alkaline.

Meanwhile, LiOH has a metal ionically bound to a covalently bound hydroxide ion. When it enters water, the strong hydrogen bonds rip apart the covalent bond between lithium and the hydroxide ion. The positively charged lithium ion is hydrated by water molecules with the oxygen end facing the lithium. And vice versa for hydroxide.

As you probably noticed, it does not dissociate into protons and a hydroxide ion. So it is alkali.

The reason hydrogen doesn't fit into the mould is because it is a non metal. And besides, the logic kinda breaks down since pH is a measure of how many protons are present relative to hydroxide ions.

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