![]() The higher oxides (peroxides and superoxides) are important oxidising agents. These are highly soluble in water giving strongly alkaline solution due to the formation of hydroxides, M + OH –, which are very largely ionised. The normal oxides of alkali metals are monoxides, M 2O. Yellow colour of sodium peroxide is most probably due to the presence of a small amount of superoxide. Note that the superoxide ion (O 2 –) has a three-electron bond which makes it paramagnetic and coloured. Structure of the three ions can be represented as below. On the other hand, the weak positive field around sodium and potassium ions allows the dispersal of the negative charge of the monoxide anion to form peroxide and superoxide ions. The increasing stability of peroxides and superoxides of alkali metals from Li to Cs is due to the fact that the strong positive field around the small lithium ion attracts the negative charge so strongly that it does not permit the monoxide anion O 2– to combine with another oxygen to form peroxide ion O 2 2–. (Na 2 O 2) and the other alkali metals form mainly superoxides (MO 2) along with a small amount of peroxides. Under ordinary conditions, lithium forms the monoxide (Li 2O), sodium forms the peroxide. Oxides: Alkali metals when heated with oxygen form oxides, the nature of which depends upon the nature of the alkali metal. Hence they are kept under an inert liquid like kerosene oil which prevents them from coming in contact with air and moisture.Ģ NaOH(s) + CO 2 (g) → Na 2 CO 3 + H 2O (l)Ģ. Action of Air: Alkali metals are so reactive that they tarnish rapidly when exposed to air because of the formation of oxides, hydroxides and ultimately carbonates at the surface. Further since the ionsation energies decrease with increase in atomic number, their reactivity also increases from Li to Cs.ġ. Due to their low ionisation energies, alkali metals are highly electropositive and chemically reactive.
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