* Calcium (Ca) is in group 2 of the periodic table, meaning it forms ions with a +2 charge (Ca²⁺).

* Oxygen (O) is in group 16, forming ions with a -2 charge (O²⁻).

To form a neutral compound, the charges must balance. A simple 1:1 ratio of Ca²⁺ and O²⁻ ions would create CaO (Calcium Oxide). There's no way to combine these ions to get a compound with the formula CaO3.