Anomalous Properties of Lithium

Being the first member of Group 1, lithium sits apart from the rest of the alkali metals in several respects, and the reason is essentially geometric: its atom and its ion are both exceptionally small, which gives $Li^+$ an unusually high polarising power (a high charge-to-radius ratio). This one structural fact is behind most of lithium's "anomalies" — most notably a marked drift towards covalent character in its compounds, which in turn explains why several lithium salts dissolve in organic solvents where the corresponding salts of the heavier alkali metals do not. …