Alkali Metals

Alkali metals are the elements of group 1 (formerly IA) of the periodic table: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr). All have a characteristic electron configuration that is a noble gas structure with one outer s-electron. They are typical metals (in the chemical sense) and readily lose their outer electron to form stable M ions with noble-gas configurations. All are highly reactive, with the reactivity (i.e. metallic character) that increases down the group. There is a decrease in ionization energy from lithium to cesium. The second ionization energies are much higher and divalent ions are not formed. Other properties also change down the group. Thus, there is an increase in atomic and ionic radius, an increase in density and a decrease in melting and boiling points. The standard electrode potentials are low and negative, although they do not show a regular trend because they depend both on ionization energy (which decreases down the group) and the hydration energy of the ions (which increases). All the elements react with water (lithium slowly; the others violently) and tarnish rapidly in air. They can all be made to react with chlorine, bromine, sulрhur and hydrogen. The hydroxides of the alkali metals are strongly alkaline (hence the name) and do not decompose on heating. The salts are generally soluble. The carbonates do not decompose on heating, except at very high temperatures. The nitrates (except for lithium) decompose to give the nitrite and oxygen:

2MNO₃(s) ® 2MNO₂(s) + O₂(g).

Lithium nitrate decomposes to the oxide. In fact lithium shows anumber of dissimilarities to the other members of group 1 and in many ways it resembles magnesium. Lithium is widely-used in batteries and also as a potential tritium source for fusion research. On heating it reacts with nitrogen and oxygen. In general, the stability of the salts of oxo acids increases down the group (i.e. with increasing size of the M⁴ ion). This trend occurs because the smaller cations (at the top of the group) tend to polarize the oxo anions more effectively than the larger cations at the bottom of the group.

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