Potassium belongs to the family of elements called the alkali metals. This is the first group of elements on the periodic table because they all are very reactive and have a single electron in their outermost energy level.
Potassium is highly reactive, readily giving away its single electron to other atoms to form compounds. If not kept separate, potassium reacts with the oxygen and water vapor in the air to form compounds.
The alkali metals are generally very soft metals. Cesium, the last of the alkali metals, is the most reactive alkali metal whereas lithium is the least reactive of the group. These elements are never present in their free forms in nature and are usually found combined with nonmetals to form ionic compounds.