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: 
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> Teacher stated that the ionic compounds dissolve in water except some carbonates.
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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. 

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> I want a clear elaboration of this phenomenon can somebody help me??
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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.
Solubility of salts is not a prediction that I like to make. It all comes down to $\Delta{G}\_{sol} < 0$. That condition is fulfilled when $\Delta{H}\_{sol} < 0$ and $T \Delta{S}\_{sol} > 0$ or one factor outweighs the other.

There's two problems. Lattice enthalpies are large, as are solvation enthalpies, and the common observation is that $\Delta{H}\_{sol}$ in most cases is small. We are calculating differences of large numbers, and the one fact we can confidently assert is that the difference is impossible to predict and generally meaningless.

Same thing for $\Delta{S}\_{sol}$. Lattice entropies are small, but entropies of solution are lower than one would think thanks to the short-range order the solvated cation imposes on the solvent. You are gaining translational entropy from dissolving the lattice and losing translational entropy from the solvent through the inner coordination shell. You are calculating differences of numbers of equal magnitude again, and just by staring at reagents it's impossible to tell which way the pendulum is going to swing and if the result is positive or negative.