Introduction

Groups 1 and 2 both belong to the s-block of the periodic table, since in every element of these two groups the last electron added enters an 's' subshell. Hydrogen, atomic number 1, is the very first element of the periodic table and sits at the top of group 1 alongside the alkali metals -- but because it differs from them in a number of important respects, it is studied on its own, in a dedicated section, before the alkali and alkaline earth metals themselves are introduced.