Which element's oxide is considered the most ionic?

The element whose oxide is considered the most ionic is magnesium (Mg). This characteristic of magnesium oxide stems from a few fundamental principles of chemical bonding and periodic trends.

Magnesium is an alkaline earth metal located in Group 2 of the periodic table. It has a higher electronegativity than its counterparts in Group 1, such as sodium (Na) and potassium (K), but it is still very low when compared to nonmetals. This relatively low electronegativity combined with its position in the periodic table gives magnesium an ability to form strong ionic bonds when it reacts with highly electronegative elements like oxygen.

Ionic compounds are typically formed between metals and nonmetals, where the metal donates electrons to the nonmetal, creating cations and anions. Magnesium readily loses two electrons to form Mg²⁺ ions, while oxygen gains two electrons to form O²⁻ ions. The large difference in electronegativity between magnesium and oxygen leads to a strong electrostatic attraction, resulting in a highly ionic character for magnesium oxide (MgO).

In contrast, while the oxides of aluminum (Al), sodium (Na), and potassium (K) also exhibit ionic characteristics, they are not as ionic as magnesium oxide.