Question: I studied the solubility of compounds in water. I have found that [calcium carbonate](http://en.wikipedia.org/wiki/Calcium_carbonate) doesn't dissolve in water. The teacher stated that the ionic compounds dissolve in water except some carbonates. What would be a clear elaboration of this phenomenon?

Answer: 
As someone said here, this:

> 
> The teacher stated that the ionic compounds dissolve in water except
>  some carbonates.
> 
> 
> 

Is indeed an oversimplification. First of all, the distinction between an "ionic compound" to other compounds isn't too defined. What your teacher probably said, or didn't say but wanted to, is that some ionic compounds easily dissolve in water. Salt (halite - NaCl) is the best example.

Calcium carbonate, in nature, also commonly dissolves. It's just not as immediate as dissolution of the more soluble ionic compounds. You are probably familiar with this phenomenon:

![picture of a cave](https://i.stack.imgur.com/FMZlp.jpg)

This forms *because* calcium carbonate dissolves. The rock is limestone, which is usually composed of pure calcium carbonate. Acidic water greatly enhances the solubility of calcium carbonate, and it doesn't even need to be highly acidic. Rain or river water that come into contact with the atmosphere absorb the $\ce{CO2}$ as $$\ce{H2O + CO2 <=> H2CO3},$$ which then facilitates calcium carbonate dissolution with $$\ce{CaCO3 + H2CO3 <=> Ca^2+ + 2HCO3-}.$$
> 
> Teacher stated that the ionic compounds dissolve in water except some carbonates.
> 
> 
> 

That is, at best, an oversimplification. Other ionic compounds such as silver sulfide are sparingly soluble in water. Note that this isn't a carbonate. 

And sodium hydrogen carbonate - $\ce{NaHCO3}$ - is soluble in water. 

Sodium carbonate ($\ce{Na2CO3}$) is also soluble in water. 

> 
> I want a clear elaboration of this phenomenon can somebody help me??
> 
> 
> 

Solubility depends on:

1) The strength of the intermolecular attractions within the solute and the strength of the solvent-solvent interactions. How strongly is the calcium ion and the carbonate ion bound together? You might *think* that the force of attraction between a +2 and a -2 ion is strong, but remember, covalent bonds are generally stronger than ionic interactions. How strong are the solvent-solvent molecule interactions - which must be broken before something can be solvated? 

2) Solvation. How well can the solvent lower the energy of the dissociated solute ions? How well can calcium ion and carbonate ion be solvated (by water in this case?) How strong are the solvent-solute ion interactions? What about the entropy of solvation? (Solvation shells are highly ordered). 

If you wish to predict the solubility of some compound, try using hard soft acid/base theory.