CBSE - XI Science - Chemistry - The s-Block Elements
why BeCO3 is thermally unstable while BaCO3 is more stable?
- The thermal stability of carbonates varies directly with the size of cation.
- The increasing order of thermal stability of carbonates is as follows:
- BeCO3 < MgCO3 < CaCO3 < SrCO3 < BaCO3
- BeCO3 is very unstable mainly because of the enhanced stability of BeO over BeCO3.
- Cations with high ionic potential have large power of polarisation. In crystalline solid, the M2+ cation is surrounded by oxygen of CO32- ions. When ionic potential of cation (such as small Be2+) a partial covalent bond is setup between M2+ and O, as a result C-O bond becomes weak due to withdrawl of electrons.
- Hence, carbonate of alkaline earths decompose into oxide and CO2. Large cations like Ba2+ have low ionic potential and are unable to polarise the electrons of O atom due to which carbonates of large cations are more stable.
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