Ncert Exercises & Solutions

Present a comparative account of the alkali and alkaline earth metals with respect to the following characteristics.

1. Tendency to form ionic/covalent compounds

2. Nature of oxides and their solubility in water

3. Formation of oxosalts

4. Solubility of oxosalts

5. Thermal stability of oxosalts

(a) Alkaline earth metlas form compounds which are predominantly ionic but less ionic than the corresponding compounds of alkali metals due to increased nuclear charge and small size.

(b) Oxides of alkaline earth metals are less basic than corresponding oxides of alkali metals. The oxides dissolve in water to form basic hydroxides and evolve a large amount of heat. The alkaline earth metal hydroxides are however less basic and less stable than alkali metal hydroxides.

(c) Alkaline earth metals form oxoacids as alkli metals. The formation of alkali metal oxoacids is much more faster and stronger than their corresponding alkaline earth metals due to increased nuclear charge and small size.

(d) Solubility of alkaline oxoacids is more than alkali oxoacids because alkaline earth metals have small size of cation and higher hydration energy. Salts like CaCO₃ are insoluble in water.

(e) Oxosalts of alkali metals are thermally more stable than those of alkaline earth metals. As the electropositive character increases down the group, the stability of carbonate and hydrogen carbonates of alkali metal increases.

Whereas for alkaline earth metals carbonate decomposes on heating to give carbon dioxide and oxygen.

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