The charge of an oxygen ion is typically -2. This is because oxygen, which is in group 6 of the periodic table, has six electrons in its outer shell. To achieve a stable electron configuration, oxygen gains two electrons, resulting in a full outer shell of eight electrons. This gain of two electrons gives the oxygen ion a net charge of -2.
In chemical terms, oxygen forms an anion (a negatively charged ion) by accepting these two electrons. This process is common in the formation of ionic compounds, where oxygen often pairs with elements that can donate electrons, such as metals.
For example, in the formation of magnesium oxide (MgO), magnesium donates two electrons to oxygen, resulting in Mg2+ and O2- ions. The electrostatic attraction between these oppositely charged ions forms the ionic bond in magnesium oxide.