* Electro negativity Difference: Aluminum (Al) is a metal, and Selenium (Se) is a nonmetal. The electronegativity difference between them is significant, leading to the transfer of electrons from the metal (Al) to the nonmetal (Se). This transfer results in the formation of ions.

* Ionic Bonding: Aluminum loses three electrons to form a +3 ion (Al³⁺), and Selenium gains two electrons to form a -2 ion (Se²⁻). The electrostatic attraction between these oppositely charged ions forms the ionic bond.

Therefore, Al₂Se₃ is an ionic compound due to the transfer of electrons and the formation of ions held together by electrostatic forces.