Hydrogen Hydroxide

Water.

Specifically, water reacting as a base. When reacting as an acid its systematic name is HydroxicAcid.

Oddly enough, water can be considered a molecule (H2O), or an ion group (H+ and OH-). Once I got that through my skull, the whole acid/base mess got much clearer.

[Surely water doesn't normally sit around ionized.]

Well, yes and no. The bond angles and resonance are consistent with water as a molecule, but the Lewis-acid/base thing won't work that way.

I have been told by a friend who has high expertise in this area that water is actually very complex, and forms fleeting groups of multiple H2O molecules (as well as all conceivable radical ions and their groupings), and that this kind of nano-structure of water is not well understood to this day, despite the fact that its macroscopic properties have been largely understood for quite a while.
One need not take such statements purely on faith; it's well known that it is quite difficult (typically intractable, with some exceptions) to infer chemical/mesoscopic properties from physics alone. The successes of reductionism from the "higher" level of chemistry to the "lower" level of physics are what are notable; in the general case, reductionism does not and cannot work due to issues of computational complexity and emergent properties that are difficult (usually completely intractable) to predict from the lower level of reductionism.
I anticipate flames from those who still hope that reductionism always works, but seriously, this sort of thing has been well-known for ages.
"Condensed Matter Physics" is one of the names of the very, very (did I say "very"? repeat a few times) difficult mesoscopic areas between atoms and baseballs. NB this is not one of my fields, but I find it interesting. -- DougMerritt

From "ChemicalPrinciples?" sixth edition by Masterton, Slowinski and Stanitski, chapter 19.1:

: The acidic and basic properties of aqueous solutions are dependent upon an equilibrium that involves the solvent, water. Water, when pure or as a solvent, tends to dissociate to some extent into hydrogen ions and hydroxide ions: H20 <-> H+(aq) + OH-(aq)

pH is the negative logarithm of the molar concentration of [H+]. (See http://www.encarta.msn.com/find/Concise.asp?z=1&pg=2&ti=761552883) Broken link At neutral pH, [H+] = [OH-] = 1E-07 mol/l.

H20 has a molecular weight of about 18 (16+1+1), so 1 mol H20 is about 18 g. The concentration of water in pure water is therefore 1000/18 = 55.6 mol/l. The concentration of [H+] at neutral pH is 1E-07 therefore the ratio of [H+] : [H2O] is 1E-07 : 55.6(*) or, 1 H+ per 55.6/1E-07 = 5.56E+08 H2O molecules ([mol/l] / [mol/l] is unitless).

(*) actually (55.6 - 1E-07) ~ 55.6

But -log(5.56E+08) is -8.75, and I'm sure I recall the pH of distilled water is about 5.6, so I think there's something amiss here ...

pH is the negative logarithm of the concentration of H+ per unit mol/L, ignoring the concentration of water. The pH of distilled water is 7, it's things like tapwater that vary from that.

Distilled water will rapidly absorb CO2 from the air forming weak carbonic acid with pH ~5.7

See http://en.wikipedia.org/wiki/Distilled_water for more.

I had learned that H+ ions actually formed weak hydrogen bonds with neutral water molecules, resulting in hydronium ions H3O+, or more generally H[H_{2}O]_{n}{+} ions.

Close, but it's not a weak hydrogen bond. Hydronium ions are genuinely H3O+, all three hydrogen atoms in them are entirely equivalent. The dissociation water undergoes into ions is actually the transfer of a hydrogen atom from one to another, giving hydronium and hydroxide, not a matter of the bonds within a molecule being partially ionic, as the name HydrogenHydroxide would suggest. And, btw, if they were than you'd expect both to be, so it would be hydrogen oxide.

However, what chemists actually use in the vast majority of cases takes precedence over what some secondary naming scheme would dictate. Just like the proper name for the neutral chemical is water, and DihydrogenMonoxide is an invention that you won't find in even the most rigorous text.

DihydrogenMonoxide is anti-environmental-regulation satire of the "everything is dangerous" school, though it fooled me for a moment the first time I read it.

Precisely the point. It's very easy to whip people into a frenzy, which is useful if you have an agenda. We should learn to examine environmental claims critically.

CategoryWater ;)