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Thermal stability of group 2 chlorides follows the order: $\ce{BeCl2>MgCl2>CaCl2}$.

Talking about carbonates of group 2 metals, the thermal stability increases as we move down the group due to decreasing polarizing power of the cations. Why is the similar trend not observed in halides? I found an answer here which had an elaborate explanation of the fazan's rule and effect of polarizability of anions. However, that comparison was made for a single cation bonded with different halogens bonded one on one as one moves down the group. Surely, the stability in that case increases down the group as the charge density on anion decreases. The comparison made here is different. I want to know the trend when the cation is being changed and anion is same. According to Fazan's rule, the trend should be same as that for carbonates: their stability increases on moving down because charge density of cation decreases. But this is not observed in the case of chlorides. Why is that so?

Sara Shanker
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  • @Willim R. Ebenezer, I went through the explanation you have shared the link of, but I still can not find an answer to my question. In that answer, the trend in stability has been examined keeping the cations same and anions changing as one moves down the group. However, I want to know the trend of keeping the anions same and cations changing. I will edit my question to get more exact. – Sara Shanker May 16 '19 at 03:45
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    I believe that has been discussed too. I quote thence: When the ions electron cloud, is less polarized, the bond is less strong, leading to a less stable molecule.. Does that not suffice? – William R. Ebenezer May 16 '19 at 05:53
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    Ohkay. I can clearly apply this concept to my problem and I now understand why does that happen. Your quote just clicked it. Thankyou:) – Sara Shanker May 16 '19 at 08:31

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