* Metals and Nonmetals: Barium (Ba) is a metal, and oxygen (O) and hydrogen (H) are nonmetals. Ionic compounds are typically formed between metals and nonmetals.

* Electrostatic Attraction: Barium loses two electrons to become a positively charged barium ion (Ba²⁺). The hydroxide ion (OH⁻) forms when oxygen and hydrogen share electrons, but the oxygen atom attracts the shared electrons more strongly, giving the hydroxide ion a negative charge. The opposite charges of the ions attract each other, forming the ionic bond.

* Crystalline Structure: Ionic compounds tend to form crystalline structures, where the ions are arranged in a repeating pattern. Barium hydroxide exhibits this characteristic.