The compound formula for Calcium (Ca) and Sulfur (S) is CaS, which is called Calcium Sulfide.

Here's how we arrive at that:

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

* Sulfur is in group 16, forming -2 ions (S²⁻).

* To balance the charges, you need one Calcium ion and one Sulfur ion. Therefore, the formula is CaS.