• # question_answer 84)   Present a comparative account of the alkali and alkaline earth metals with respect to following characteristics:       (i) Tendency to form ionic/covalent compounds. (ii) Nature of oxides and their solubility in water. (iii) Formation of oxosalts. (iv) Solubility of oxosalts. (v) Thermal stability of oxosalts.

 Characteristic Alkali metals Alkaline earth metals 1. Tendency to form ionic/covalent compounds. Except lithium, the compounds of alkali metals are ionic. Li compounds are somewhat covalent due to small size of ion (high polarising power). These are less electropositive than al- kali metals. Except Be and Mg, other elements form ionic compounds. Be and Mg compounds are somewhat covalent in nature. 2. Nature of oxides and their solubility in water. Oxides are basic, combine with water and form strong alkalies. Basic nature in- creases gradually as the atomic number in- creases. Except $BeO$other MO oxides are basic. They combine with water and form basic hydroxides. The basic nature in-creases from top to bottom, less basic than the oxides of alkali metals, $BeO$and $MgO$ are insoluble in water. 3. Formation of oxo- salts. React readily with oxy acids and form oxo salts. Salts are colourless, crystalline and ionic in nature. React with oxy acids and form salts. Salts are colourless, crystalline and ionic in nature except Be salts. 4. Solubility of oxosalts:   Carbonates. Bicarbonates. Nitrates. Sulphates. Carbonates are highly soluble in water. Known in free state. Soluble in water. Soluble in water. Soluble in water. Carbonates are insoluble in water.   Only known in solution. Do not exist in solid state. Soluble in water. Solubility decreases $BeS{{O}_{4}}$, $MgS{{O}_{4}}$ are soluble, $CaS{{O}_{4}}$ is sparingly soluble while $SrS{{O}_{4}}$ and $BaS{{O}_{4}}$are insoluble. 5. Thermal stability of oxosalts: Carbonates. Nitrates.   Sulphates. Stability increases. only $L{{i}_{2}}C{{O}_{3}}$decomposes. Except $L{{i}_{2}}C{{O}_{3}}$ decompose into nitrite and oxygen. Stable towards heat. Less stable decompose into oxide and $C{{O}_{2}}$stability increases. Decompose into $N{{O}_{2}}$ and ${{O}_{2}}$ besides oxide. Decompose on heating to oxide, $S{{O}_{2}}$ and${{O}_{2}}$.