Chlorine has an outer shell of seven electrons. To get a full outer shell one electron each is gained by two chlorine atoms forming 2 chloride ions with a single negative charge.Calcium has two outer shell electrons, the outer shell is incomplete so not stable therefore these two electrons are transferred to another atom, forming a stable calcium ion with a charge of +2 .The formula of calcium chloride is $\mathrm{CaCl}_2$.Thus, the correct electron dot structure of $\mathrm{CaCl}$, is