Characteristics of s-Block Elements

The s-block consists of group 1 (the alkali metals) and group 2 (the alkaline earth metals). All of these elements are highly reactive metals and, as a result, are never found free in nature — always in some combined (compound) state. With only one or two valence electrons that are readily lost, they form predominantly ionic compounds, the sole exceptions being lithium and beryllium (whose small size and high charge density give their bonds significant covalent character instead). Because they lose electrons so readily to form $M^+$ (group 1) or $M^{2+}$ (group 2) ions, s-block elements have characteristically low ionization enthalpies; these enthalpies decrease further down each group (per the atomic-radius and screening trends of section 7.5), which is why reactivity of …