Short Answer TypeThe ionic radii of alkali metal ions in aqueous solution follows the order Li+ > Na+> K+ > Rb+ > Cs+ Justify the above order.
Long Answer TypeDiscuss the general trends in ionisation enthalpy and electropositive character of alkali metals.
Short Answer TypeLithium ion has the lowest and caesium ion has the highest mobility in an electric field. Explain.
When an alkali metal dissolves in liquid ammonia the solution can acquire different colours. Explain the reactions for this type of colour change.
Or
Explain why alkali metals dissolve in liquid ammonia to form deep blue solution.
How will you explain that alkali metals are chemically highly receive?
Due to low values of first ionisation enthalpies, low heats of atomization and high hydration enthalpies, alkali metals lose their valence electron readily and hence are chemically highly reactive.
Their relative tendency to lose electron in chemical reactions depends on upon:
(i) Ionisation enthalpy: Lower the ionisation enthalpy, greater the chemical reactivity.
(ii) Hydration enthalpy: Larger the hydration enthalpy, greater the chemical reactivity.
Now ionisation enthalpies of alkali metals decrease down the group and hence chemical reactivity increases. Also, hydration enthalpies of alkali metals increase down the group and so chemical reactivity increases. Hence, the chemical reactivity increases down the group of alkali metals. Thus, caesium (Cs) is the most reactive among the alkali metals i.e. Cs has maximum tendency to lose the valence electron to form monovalent Cs+ ions.
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