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

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

• Are you asking this with regards to the dissolution of inorganic salts? – Tan Yong Boon Dec 2 '18 at 13:23
• – Mithoron Dec 2 '18 at 20:26

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).