Chemistry: Why does thermal stability of S-block carbonates increase down the groups?

Question

I know that the thermal stability of the S-block carbonates increases down each group. Down group 2, cation size increases, while the charge on each ion stays the same. Charge density therefore decreases and the cation is less able to polarise the anion...the degree of covalency therefore decreases down the group.. and thermal stability increases.

Does this imply that covalent bonds are weaker than ionic bonds?

Also, the group 2 chloride experimental lattice enthalpies are higher than the predicted values. The difference between the two decreases as you go down the group (i.e. as covalency decreases)....bond polarisation increases...more energy is needed to break the bonds in the lattice than predicted......doesn't this suggest that covalent bonds are stronger than ionic bonds??

In short,
If anyone can explain why the thermal stability of S-block carbonates increases down groups 1 and 2, I would be very grateful.

Answer 1

Yoo should consider the stability of the oxides (to which the carbonates would decompose, if heated) relative to the carbonates. You will find that the carbonates become more and more stable as you go down the group.

There is nothing inherently weak about covalent bonds.

Answer 2

u have made me think as well.......... i think u r rite......... i have read s-block yet even it has been tought 2 me a month back.... i think i should start studying.....