Cesium is a member of the alkali family, which consists of elements in Group 1 (IA) of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. The alkalis include lithium, sodium, potassium, rubidium, and francium. Cesium is considered the most active metal.esium is a member of the alkali family, which consists of elements in Group 1 (IA) of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. The alkalis include lithium, sodium, potassium, rubidium, and francium. Cesium is considered the most active metal.