The normal oxides contain the oxide ion, O^2- which is an extremely strong base. Hence, they react with water to form hydroxide by proton exchange as:

The alkali metal hydroxides are the strongest bases known. The strength of a base depends on the separation of hydroxide ion form the cation. Two factors are mainly responsible for the separation of hydroxide ion from cation as :

(a)    Polarity of bond. The greater the polarity of the bond, the greateris the ease of ionization. The alkali metal hydroxides do not greatly differ in polarity and this factor is not of much singifincae here.

(b)    The internuclear distance between the oxygen of the hydroxide and the metal atom. Since the cation size increase form lithium to cesium, hence, inter-nuclear distance increases with increasing atomic number of the metal. This resulays in greater separation of hydroxide ion form the metal ion. Consequently, the separation between he metal ion and OH^- ion becomes easier. Therefore, the strength of the bases increases from LiOH to CsOH.

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