The group of metals characterized by a single valence electron and are very reactive atoms are the alkali metals.

Here's why:

* Single Valence Electron: Alkali metals have only one electron in their outermost shell, making them highly eager to lose this electron and achieve a stable, full outer shell configuration.

* High Reactivity: This tendency to lose an electron makes them highly reactive. They readily react with water, oxygen, and other nonmetals to form ionic compounds.

Examples of alkali metals include:

* Lithium (Li)

* Sodium (Na)

* Potassium (K)

* Rubidium (Rb)

* Cesium (Cs)

* Francium (Fr)