* Metals and Nonmetals: Aluminum (Al) is a metal, and nitrate (NO₃⁻) is a polyatomic ion composed of nonmetals (nitrogen and oxygen). Ionic compounds are typically formed between metals and nonmetals.

* Electrostatic Attraction: Aluminum readily loses three electrons to form a +3 cation (Al³⁺). Nitrate gains one electron to form a -1 anion (NO₃⁻). The electrostatic attraction between these oppositely charged ions holds the compound together.

* Formula Unit: The formula for aluminum nitrate is Al(NO₃)₃, indicating that three nitrate ions are needed to balance the charge of one aluminum ion.

Let me know if you'd like more examples of ionic and covalent compounds!