This might be a little difficult to explain but I'll try. Here's the thing, as you go down the group, the polarisation power decreases. Now, you're probably thinking 'That should make the bond weaker'. But the deal is that carbonates and nitrates are not single atoms. The more polarised they are, the more uneven charge density they have because the cation is mainly pulling just one oxygen atom towards itself. This makes the other part of the carbonate or nitrate ion unwilling to stay with the cation. The more you go down group 2, the more the charge density becomes even around the carbonate or nitrate ion as it is less polarised and the ion is more willing to stay with the cation. So as you go down the group metal carbonates and nitrates become more stable. Hope my explanation didn't confuse you too much.
lol i did get confused a bit..but yeah that helped..so thnaks bro..
well also we need to think about the other possible factors too right..like the atomic radii...lattice and hydration enthalpies...
if the attraction is large( atomic radius is less) then a lot of energy will be given out when the lattice is formed from the ions and so the lattice energy wil have a large -ve value..
as we go down the group the value becomes positive..
the lattice energies also fall at diffrnt rates..like for eg: oxide ion is smaller than carbonate ion so its lattice enthalpy will fall faster...
so basically this is the thing right..that as u go down the group..the lattice enthalpy becomes more positive so a great deal of energy is needed to break it down(decompose) n so its stable..
and oh yeah whts with those exceptions everywhere lithium carbonate na dlithium nitrate...
thanks alot bro!
