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While studying in high school, I came across the following thermal decomposition reactions:

$$\ce{Li2CO3 -> Li2O + CO2 }$$ $$\ce{MgCO3 -> MgO + CO2}$$ $$\ce{PbCO3 -> PbO + CO2}$$

$$\ce{Ag2CO3 -> 2 Ag + CO2 + ½ O2}$$ $$\ce{HgCO3 -> Hg + CO2 + ½ O2}$$

Basically, some metal carbonates decompose into their metal forms, while others decompose into their oxides.

Furthermore, alkali metal carbonates don't decompose at all, with the exception of Lithium.

I noticed a similar pattern in metal nitrates as well, where $\ce{AgNO3}$ decomposes into $\ce{Ag}$, but $\ce{Pb(NO3)2}$ decomposes into $\ce{PbO}$.

I want to know why is this so, and what other metals fit in such categories.

I tried looking it up in certain literature, but couldn't find any information other than the periodic trends of thermostability. One classmate suggested the Hard acid and base concept, but that too left me unsatisfied for an answer.

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