Calcium is an alkaline metal and its symbol is Ca. Iodine is a halogen and its symbol is I. There are two atoms present in the valence shell of calcium and calcium loses two electrons to become stable. Therefore, the valency of calcium is +2. Iodine has seven electrons in valence shell and requires one electron to complete outer most shell. So, the valency of iodine is -1. Calcium is combined with iodine to forms calcium iodide. Calcium transfers two electrons to two atoms of iodine. It can be expressed as;
Ca ------ > Ca+2 + 2e-
2I + 2e- ------ > 2I-
Ca+2 + 2I- ------ > CaI2
Ca ------ > Ca+2 + 2e-
2I + 2e- ------ > 2I-
Ca+2 + 2I- ------ > CaI2