The compound that forms between calcium (Ca) and nitrogen (N) is calcium nitride (Ca₃N₂).

Here's how to determine the formula:

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

* Nitrogen is in group 15, meaning it forms a -3 anion (N³⁻).

* To balance the charges, you need three calcium ions (3 x +2 = +6) and two nitrogen ions (2 x -3 = -6).

Therefore, the formula for calcium nitride is Ca₃N₂.