Why do large cations stabilise large anions and small cations stabilise small anions? [closed]








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I see this trend from enthalpy change of decomposition data, though I struggle to find a decent explanation for why.




For more detailed info, search "cation-anion radius ratio" or "Pauling's rules". Below is my review of this idea. 


This ratio is ${R\_{C}/R\_{A}}$ (C = cation, A=anion). 


Small cation (I mean, **too small**) attracts anions in such a way that they come too close to each other and repulsive force comes into play. This happens when ratio is <0,155. So for larger anion, larger cation suits better. Ratio can be 0.155-1 for stable compounds, and this ratio also determines coordination number and type of void! (Check the picture below, recall that since <0.155 ratio is for unstable compounds, you have empty "example" line there).


[![enter image description here](https://i.stack.imgur.com/DbFq9.png)](https://i.stack.imgur.com/DbFq9.png)


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