Why isn't ##Li_2CO_3## (lithium carbonate) soluble in water?

Lithium carbonate is slightly soluble in water.

Actually, lithium carbonate is slightly soluble in water, its solubility at ##25^@"C"## being listed at ##"1.3 g/100mL"##.

However, lithium carbonate is not very soluble compared with other lithium salts or with other alkaline earth metal carbonates.

That happens because of lithium's small .

The strength of the electrostatic attraction that exists between the cations and anions that make up an is directly proportional to the charge of the ions and inversely proportional to the distance between these ions.

This means that, when charges are kept constant, like you get for alkaline earth metal carbonates, the most important is the size of the alkaline earth metal ions.

Alkaline earth metals that have larger cations will be more soluble because of the decreasing strength of the electrostaic force of attraction.

SImply put, lithium carbonate is less soluble because the electrostatic attraction between the very small lithium cation and the carbonate anion overpowers the attraction between these ions and the water molecules.