* Sodium (Na) is a metal, and metals tend to lose electrons to form positive ions (cations). In this case, sodium loses one electron to become Na⁺.

* Oxygen (O) is a nonmetal, and nonmetals tend to gain electrons to form negative ions (anions). Oxygen gains two electrons to become O²⁻.

To form a neutral compound, the charges must balance. Two sodium ions (2Na⁺) with a total charge of +2 will balance the charge of one oxide ion (O²⁻). This results in the ionic compound sodium oxide (Na₂O).