Here's why:

* Cations are positively charged ions formed when an atom loses electrons.

* Anions are negatively charged ions formed when an atom gains electrons.

* Ionic compounds are formed by the electrostatic attraction between oppositely charged ions.

In aluminum oxide (Al₂O₃), aluminum (Al) forms a +3 cation (Al³⁺), while oxygen (O) forms a -2 anion (O²⁻). The compound forms when these ions combine in a ratio that balances the charges: 2 aluminum ions (2 x +3 = +6) and 3 oxygen ions (3 x -2 = -6).

Symbol: Al₂O₃