Lithium carbonate is less stable than sodium carbonate since
Li is less electropositive than
Na. As lithium carbonate is not stable to heat, it decomposes at lower temperature. Small sized Li polarizes large carbonate ion which leads to formation of Li2O and CO2. Since, sodium carbonate is very stable, it decomposes at high temperature.
I found some important
information here, see the part on thermal stability:
Physical state: * Carbonates and bicarbonates are solids at room temperature. Carbonates of group-1 and group-2 elements are colorless. Whereas, the carbonates of transition elements may be colored.
* The polarizing power of the group-1 metal ions (M+) is less than the polarizing power of group-2 metal ions (M2+). Hence group-2 carbonates are more covalent than the carbonates of group-1.
Whereas the polarizing power decreases down the group with increase in the size of metal ion. Hence the ionic nature increases down the group.
Solubility in water:* Except Li2CO3, The group-1 carbonates are fairly soluble in water. The solubility increases down the group as the ionic nature nature increases.
* Group-2 carbonates are sparingly soluble in water as their lattice energies are higher (it is due to increase in covalent nature). There is no clear solubility trend observed down this group.
But group-2 carbonates are soluble in a solution of CO2 due to formation of HCO3-.
Thermal stability:* Carbonates are decomposed to carbon dioxide and oxide upon heating. Whereas bicarbonates give carbonate, water and carbon dioxide.
* Thermal stability of group-1 and group-2 carbonates (also of bicarbonates) increases down the group as the polarizing power of the metal ion decreases.
* Due to same reason, carbonates of group-1 are more stable than those of group-2.
* Small and highly charged metal ions possess more polarizing power and hence facilitates the decomposition of carbonate ion into carbon dioxide and oxide ion.
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