[Ross96]

Hi! I don't know how i can explain alkali metals carbonate stability.



I know it is related to ionic radios but I want a better explanation

Thanks!

[Babcock_Hall]

Your question is somewhat unclear.  Is this a homework assignment?  Do you main ionic radii (radii is the plural of radius)?  Can you explain what you mean by stability?

[Ross96]

I mean thermal stability. I suppose it's related to reticular energy

[Corribus]

http://www.chemguide.co.uk/inorganic/group2/thermstab.html

[Flatbutterfly]

MCO3: “… the temperature at which the carbonate reaches a dissociation pressure of 1 atm CO2 is:
BeCO3, 250°, MgCO3 540°, CaCO3 900°, SrCO3 1289°, BaCO3 1360°.”
N. N. Greenwood, A. Earnshaw, Chemistry of the Elements 2nd ed. (1997) p 114.

I believe this is an example of a larger cation stabilizing a large anion (i.e., CO3^2-).  A larger cation allows better contact with the carbonate ion and reduces repulsion between the anions.  This results in ground-state stabilization to the activation energy needed to cause CO2 dissociation.