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  Inorganic Chemistry

Oxidation number and valency

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(i) Alkali metals are univalent in nature due to low ionisation energy values and form ionic compounds. Lithium salts are, however, covalent.

(ii) Further, the M+ ion acquires the stable noble gas configuration. It requires very high values of energy to pull out another electron from next to outer shell of M+ ion and that is why their second ionisation energy is very high. Consequently, under ordinary conditions, it is not possible for these metals to form M2+ ion and thus they show +1 oxidation state.

 

(iii) Since the electronic configuration of M+ ions do not have unpaired electron and thus alkali metal salts are diamagnetic and colourless. Only those alkali metal salts are coloured which have coloured anions e.g. K2Cr2O7 is orange because of orange coloured Cr2O72- ion, KMnO4 is violet because of violet coloured MnO41- ion.

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