The most active metals in the activity series are lithium, sodium, rubidium, potassium, cesium, calcium, strontium and barium. These elements belong to groups IA and IIA of the periodic table of elements.
In terms of relative reactivity, metallic elements are classified into four groups: active, less active, structural and coinage. Active metals are characterized by their tendency to readily combine with gaseous oxygen and atmospheric water vapor. Due to this highly reactive nature, these elements are commonly stored in an inert fluid material, such as petroleum-derived oil.
Less active metals include magnesium, zinc, aluminum and manganese. Although these elements are not likely to bond with water at normal temperatures, less active metals quickly combine with acidic compounds.