Calcium is a chemical substance and its symbol is Ca. The atomic number and atomic mass of calcium is 20 and 40 respectively. Calcium is an alkaline earth metal and present in the s-block of the periodic table. Calcium lies in 2nd group and 4th period of the periodic table. The electronic configuration of calcium is 4s2. The number of electrons present per shell in a calcium atom is 2, 8, 8, 2. Calcium has two electrons in its outer most shell. To complete it outer most shell and to become stable calcium atom losses two electrons. When calcium atom loses electrons, it becomes calcium ion. The number of electrons per shell in a calcium ion is 2, 8, 8.