General Characteristics of the Compounds of the Alkali Metals.

1.	General Characteristics of the Compounds of the Alkali Metals.
Answer» Solution :On combustion in excess of air, lithium forms mainly the oxide, `Li_(2)O`(plus some peroxide `Li_(2)O_(2)`), sodium forms the peroxide, `Na_(2)O_(2)` (and some superoxide `NaO_(2)` ) whilst potassium, rubidium and caesium form the superoxides, `MO_(2)` . Under appropriate conditions pure compounds `M_(2)O, M_(2)O_(2) and MO_(2)` may be prepared. The increasing stability of the peroxide or superoxide, as the SIZE of the metal ion INCREASES, is due to the stabilisation of large anions by LARGER cations through lattice energy effects. These OXIDES are easily hydrolysed by water to form the hydroxides. The oxides and the peroxides are colour less when pure, but the superoxides are yellow or orange in colour. The superoxides are also paramagnetic. Sodium peroxide is widely USED as an oxidising agent in inorganic chemistry.

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