↪ When alkaline earth metal carbonates and nitrates are heated, they decompose to give metal oxides as,
↪ The oxides ion are more strongly attracted to metal ions in the crystals lattice than CO32- and NO3- ions because the charge density in small O2- ion is greater than that in large ions, CO32- and SO42-.
↪ Therefore alkaline earth metal carbonates and nitrates are decomposed thermally to give more stables crystals of metal oxides.
↪ The general trend of stability of carbonates and nitrates is described briefly:
1. Stability of carbonate
↪ Carbonates of alkaline earth metals are fairly stable to heat.
↪ The thermal stability of carbonates goes on increasing from top to bottom along group.
The general trend is:
BeCO3 < MgCO3 < CaCO3 < SrCO3 < BaCO3
2. Stability of nitrate
↪ The thermal stability of metal nitrates increases from top to bottom in the group.
↪ The general trend of thermal stability of nitrates is:
Ba(NO3)2 > Sr(NO3)2 > Ca(NO3)2 > Mg(NO3)2 > Be(NO3)2