* Electronegativity Difference: Copper (Cu) is a metal with a relatively low electronegativity, while oxygen (O) is a nonmetal with a high electronegativity. The difference in electronegativity between copper and oxygen is significant, leading to a transfer of electrons.

* Electron Transfer: Oxygen has a strong attraction for electrons, so it pulls electrons away from copper. This results in copper losing electrons and becoming a positively charged cation (Cu²⁺), while oxygen gains electrons and becomes a negatively charged anion (O²⁻).

* Electrostatic Attraction: The oppositely charged ions attract each other through electrostatic forces, forming an ionic bond.

Therefore, the strong electrostatic attraction between the positively charged copper ions and the negatively charged oxygen ions in copper oxide constitutes an ionic bond.