Final answer:
The ionic compound formed from calcium (Ca2+) and phosphide (P3-) ions is calcium phosphide, with the balanced formula Ca3P2.
Step-by-step explanation:
The ionic compound that would form when calcium (Ca2+) and phosphide (P3-) ions come together is calcium phosphide, with the formula Ca3P2. When creating the formula for an ionic compound, one must ensure that the total positive charge equals the total negative charge to produce an electrically neutral compound.
Calcium has a charge of 2+ and phosphide has a charge of 3-. To balance the charges, we need three calcium ions (each 2+) to balance with two phosphide ions (each 3-).
The formula Ca3P2 reflects this balance, indicating there are three calcium ions to every two phosphide ions.