Final answer:
The chemical formula for one calcium atom for every two chlorine atoms is CaCl2, which represents calcium chloride, an ionic compound formed by the transfer of electrons from calcium to chlorine.
Step-by-step explanation:
The chemical formula for one calcium atom for every two chlorine atoms is CaCl2. In this compound, calcium donates two electrons, one to each chlorine atom. The resulting ions, Ca2+ and Cl−, create a compound where the oppositely charged ions attract one another to form calcium chloride. When writing the formulas of ionic compounds involving polyatomic ions, parentheses must be used if more than one polyatomic ion is needed to balance the overall charge. For instance, the chemical formula between calcium ions, Ca2+, and nitrate ions, NO3−, is written as Ca(NO3)2, not CaNO32 or CaN2O6.