question_answer 70)

  Discuss the trend if the following : (a) Thermal stability of carbonates of group 2 elements. (b) The solubility and nature of oxides of group 2 elements.

Answer:

  (i) Carbonates of alkaline earth metals decompose on heating into corresponding oxide and\[C{{O}_{2}}\]. The thermal stability increases from top to bottom in the group. Increasing stability can be explained on the basis of decreasing polarising power and covalent character. The stability increases as the size of the cation increases gradually which can easily stabilise the bigger \[CO_{3}^{2-}\]ion. (ii) All the members of group 2 form oxides of the type MO. Barium and radium form peroxides also. Except\[~BeO\], which is amphoteric, other MO oxides are basic in nature as they combine with water to form basic hydroxides. \[MO+{{H}_{2}}O\to M{{(OH)}_{2}}\] Basic nature of the oxides increases gradually from \[BeO\]to\[BaO\]. \[BeO\]and\[MgO\] are insoluble in water on account of high lattice energies while the solubility of other oxides increases gradually.