Cesium is a chemical element and its symbol is Cs. It is an alkali metal and its atomic number is 55. The atomic mass of cesium is 132.90 grams per mole. There are 55 electrons present in one atom of cesium. The electronic configuration of cesium atom is 6s1. The number of electrons present in per shell of cesium atom is 2, 8, 18, 18, 8, 1. There is one electron present in valence shell of cesium atom. Cesium atom loses one electron to become stable or to complete its outer most shell. When cesium atom loses an electron, it gets the electronic configuration of nearest noble gas.