This is an example of ionic bonding, meaning that the cation (calcium) will lose electrons and the anion (chloride) will gain electrons so all ions will have a full outer shell.Calcium will form a 2+ ion, meaning that it will lose 2 electrons to gain a full outer shellChloride will form a 1- ion, meaning that it will gain 1 electron per chlorine atom to gain a full outer shellIn order to balance the number of lost electrons to the number of gained electrons, two chlorine atoms will form two chloride ionsTherefore, one lost electron from calcium will go to one chlorine atom and the other lost electron will go to the other chlorine atom.