* Ionic bonds form between metals and nonmetals. Calcium (Ca) is a metal, and oxygen (O) and hydrogen (H) are nonmetals.

* Calcium readily loses two electrons to form a +2 cation (Ca²⁺).

* Hydroxide (OH⁻) is a polyatomic ion with a -1 charge.

* To form a neutral compound, two hydroxide ions (OH⁻) are needed to balance the +2 charge of the calcium ion.

* The electrostatic attraction between the positively charged calcium ions and the negatively charged hydroxide ions forms the ionic bond.