Survey of the alkali metals

The alkali metals — lithium, sodium, potassium, rubidium, cesium, and francium — are members of Group 1 of the Periodic Table, and each has a single ns1 valence electron outside a rare gas core in its ground state. Some important properties of alkali metals are given in Table 12.1.1. 

The radii of the metals increase with increasing atomic number and their atomic sizes are the largest in their respective periods. Such features lead to relatively small first ionization energy (/1) for the atoms. Thus the alkali metals are highly reactive and form M+ ions in the vast majority of their compounds. The very high second ionization energy (I2) prohibits formation of the M2+ ions. Even though the electron affinities (T) indicate only mild exothermicity, M- ions can be produced for all the alkali metals (except Li) under carefully controlled conditions. 

The chemistry of the alkali metals has in the past attracted little attention as the metals have a fairly restricted coordination chemistry. However, interesting and systematic study has blossomed over the past 25 years, largely prompted by two major developments the growing importance of lithium in organic synthesis and materials science, and the exploitation of macrocyclic ligands in the formation of complexed cations. Section 12.4 deals with the use of complexed cations in the generation of alkalides and electrides. 

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