[Foobarz]

Why are ionic oxides basic in water and why are covalent oxides acidic in water?

Ex. Na₂O becomes NaOH in water

CrO₃ becomes H₂CrO₄ in water (the high oxidation number of the Cr makes it more covalent)

CO₂ becomes H₂CO₃ in water
But CO (C has a lower oxidation number and is therefore not as covalent) is not acidic in water

Is there some sort of bonding principle that explains why all these occur?

[Borek]

When it comes to ionic oxides situation is rather obvious - O^2- is a very strong Bronsted base.

[Foobarz]

What about covalent oxides? How come the more covalent it is the more acidic it is as an oxide?

[Olympiad_Tutor]

a strong acid is something that easily loses H+. in other words, its anion does not interact strongly with H+. we would like to have an anion with a low negative charge and/or low negative charge density.  if you add enough oxygen atoms you can get a bulky anion with the negative charge spread over a large surface area (low charge density).

[Foobarz]

But acidic oxides aren't anions. . .

So why does something like CO₂ with high oxidation state become carbonic acid in solution

But CO with low oxidation state does not?

[Foobarz]

*Ignore me, I am impatient*!

[UG]

But acidic oxides aren't anions. . .

Indeed, but when you add water, you form anions, e.g. H₂CO₃ and H₂CrO₄, they all have anions (carbonate and chromate anion respectively)

But CO with low oxidation state does not?

CO is almost insoluble under normal conditions, I believe if the pressure is high enough, you can get a solution of formic acid, HCOOH.

[fuyuki_kaze]

according to my book

oxide + H2O ->
Na2O          ->      basic (NaOH)
MgO           ->      basic (Mg(OH)2)
Al2O3         ->      amphoteric     (doesn't react)
SiO2          ->       acidic            (doesn't react) (yea, i know this is strange...but it is)
P4O10        ->      acidic (H2PO4)
SO3           ->      acidic (H2SO4)
Cl2O7          ->     acidic (HClO4)

[fuyuki_kaze]

according to my book

bonding      oxides
character    + H2O ->
ionic           Li2O     -> basic

both        BeO        -> amphoteric

               B2O3       ->acidic
covalent  CO2        ->acidic
               NO2        ->acidic
               OF2        ->acidic
             Na2O       ->      basic (NaOH)
 ionic     MgO         ->      basic (Mg(OH)2)
             Al2O3       ->      amphoteric     (doesn't react)

               SiO2        ->       acidic            (doesn't react) (yea, i know this is strange...but it is)
covalent  P4O10     ->      acidic (H2PO4)
               SO3         ->      acidic (H2SO4)
               Cl2O7          ->     acidic (HClO4)

so s-block metal oxides tend to form basic solution
and p-block oxides tend to form acidic solution

i wish these data would help

also for the CO and CO2 problem
i think CO and CO2 is different in the ground state of C and excited state of C
i think OH- is not enough to get the carbon monoxide's carbon from ground state to excited state but oxygen can
but for the CO2, its already in excited state and very happy to form [CO3]2-
o, the excited state and ground state is about promoting electrons to higher potential... well go for some inorganic chemistry reference books should help