why BeCO3 is thermally unstable while BaCO3 is more stable?

Asked by bhuveshsharma1317 | 8th Jun, 2016, 07:36: PM

Expert Answer:

  • 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.  

Answered by Prachi Sawant | 9th Jun, 2016, 11:00: AM