The thermal stability of alkaline earth metal carbonates () increases down the group (). What is the primary electrostatic reason for this trend?

Question

The thermal stability of alkaline earth metal carbonates ($MCO_3$) increases down the group ($BeCO_3 < MgCO_3 < CaCO_3 < SrCO_3 < BaCO_3$). What is the primary electrostatic reason for this trend?

Prashant Kotian · Accepted Answer

Correct answer: B. According to Fajans' rules, a smaller cation (like ) has high polarizing power. It heavily distorts the electron cloud of the large polyatomic ion, weakening the C-O bond and facilitating decomposition into and . Larger cations have lower polarizing power, thus increasing thermal stability.

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