Question

The thermal stability of $MC{O_3}$is in order:
A.$BeC{O_3} < MgC{O_3} < CaC{O_3} < SrC{O_3} < BaC{O_3}$
B.$MgC{O_3} < BeC{O_3} < CaC{O_3} < SrC{O_3} < BaC{O_3}$
C.$CaC{O_3} < SrC{O_3} < BaC{O_3} < BeC{O_3} < MgC{O_3}$
D.$BaC{O_3} < SrC{O_3} < CaC{O_3} < MgC{O_3} < BeC{O_3}$

Answer 1

To answer this question you must recall the trends of properties in the periodic table. We know that as we move down the group, electronegative character of elements decreases due to increase in the size of the atoms.

Complete step by step answer:
As we go from $Be$ to $Ba$ in the group, the size of the metal atoms keeps on increasing due to the addition of a new shell in each atom. Thus, the valence electrons are more loosely held increasing the metallic character of the metal atoms. Or we can also say, that in the compounds formed by alkaline earth metals, as the size increases the bond pair is increasingly farther from the nucleus of the metal and closer to the more electronegative atom thus resulting in increased stability of the compound.
Group 2 metal carbonates on heating undergo decomposition to form the metal oxide and release carbon dioxide gas. Stronger is the bond between the metal and the carbonate group more is the thermal stability of the metal carbonate. Thus, as we move down the group, the thermal stability of group 2 metal carbonates increases.
Thus, the order of the thermal stability is $BeC{O_3} < MgC{O_3} < CaC{O_3} < SrC{O_3} < BaC{O_3}$.

Thus, the correct answer is A.

Note:
Group 2 metals are known as known as alkaline earth metals as they form alkaline oxides and are unaffected by the heat of the earth’s crust. The elements present in the group 2 of the periodic table are Beryllium, Magnesium, Calcium, Strontium, Barium and Radium. Radium is generally not considered for the majority of the discussions due to its radioactive nature. All these metals have two valence electrons and thus show an oxidation state of $+ 2$.