* Electron Configuration: Oxygen has six valence electrons (electrons in its outermost shell). It wants to achieve a stable octet configuration (eight electrons) like the noble gases.
* Gaining Electrons: To achieve this stable configuration, oxygen tends to gain two electrons, which gives it a -2 charge.
* Ionic Compounds: In ionic compounds, oxygen usually forms a -2 ion (O²⁻) by gaining two electrons. This happens because the electronegativity of oxygen is very high, meaning it strongly attracts electrons.
* Covalent Compounds: In covalent compounds, where electrons are shared, oxygen still typically has a -2 oxidation state. This means it "controls" or attracts the shared electrons more strongly than the other atom it's bonded to.
Exceptions:
* Peroxides: In peroxides (like hydrogen peroxide, H₂O₂), oxygen has a -1 oxidation state. This is because oxygen forms a single bond with another oxygen atom, sharing one electron each.
* Superoxides: In superoxides (like potassium superoxide, KO₂), oxygen has a -1/2 oxidation state. This is due to the formation of a special bond between oxygen atoms.
* Fluorine: Oxygen can have a positive oxidation state when it bonds with the highly electronegative element fluorine.
In summary: While oxygen's -2 charge is not always a hard-and-fast rule, it's a very common and useful generalization for understanding the behavior of oxygen in chemical compounds.
