# Why Hg doesn’t form hydroxide?

In my textbook it was written that if you put alkali solution into Hg2+ solution you won't get Hg(OH)2 but you get HgO.
And this is because Hg has high electronegativity and this makes polarization of O-H in virtual Hg(OH)2 big enough to make dehydration of Hg(OH)2.

I couldn't understand the reason well. Dehydration seems like a kind of neutralization because it emit H2O and makes salt(HgO), but neutralization between the same thing(in this case Hg(OH)2 )is usually not favored (reaction like 2HCO3-->H2O+CO2+CO32- is not favored.) Why Hg(OH)2 dehydration favored ? Electronegativity of Hg is 2.0(Pauling) and 2.2(H) so it is smaller in Hg actually.

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• The core 5d orbitals of Hg are relatively close in energy to the valence oxygen orbitals and repel them. Sep 27, 2022 at 1:46
• @KanghunKim how does that explain formation of HgO over Hg(OH)2? In both of them oxygen is binding to Hg. Sep 27, 2022 at 3:48
• An Hg can barely mind binding to one oxygen(HgO is actually only kinetically stable)- it just cannot withstand binding to TWO oxygens. Sep 27, 2022 at 14:30
• Suppose that you get an upset stomach to apples. Eat one apple and you're barely trying not to throw it up(but it gets wasted as diarrhea at some time). This is HgO. Eat two apples and you throw half up(Hg(OH)2 -> HgO + H2O), later you excrete the other half as diarrhea. Not a metaphor that agrees with the table, but you get the idea. Sep 27, 2022 at 14:33