What characterizes alkali metals?

The defining characteristic of alkali metals is that they have one valence electron in their outermost electron shell, which makes them highly reactive. This single electron is easily lost during chemical reactions, leading these metals to form strong bonds with other elements. Because of this reactivity, especially with water, alkali metals are typically found in nature only in compound forms rather than in their elemental states. Their reactivity increases as you move down the group in the periodic table, meaning that cesium is more reactive than lithium, for instance. This characteristic one valence electron greatly influences their chemistry and accounts for their positioning in group 1 of the periodic table.