Why does oxygen have variable oxidation numbers in oxides peroxides and super-oxides?

Answer 1

Oxygen, and many other elements, especially the transition and actinide metals, can form compounds in which it has a variety of oxidation states. Oxygen may have various oxidation numbers depending on whether it is O2, O3 or what is has reacted with. For example, potassium can donate one electron to O2 to form KO2, potassium superoxide. Except for the superoxide ion, an oxygen atom has a completed octet of electrons and all the electrons are paired. In other words, all of the atomic or molecular bonding orbitals are filled with two spin-paired electrons so that the total of shared and unshared electrons is eight. This is the most stable electronic configuration of oxygen.

The superoxide ion, O2-, is a resonance-stabilized radical, and as such it is generally more reactive (a more powerful oxidizing agent) than the other oxygen species above as it will more easily oxidize (remove an electron from) other species in order for the oxygen with seven electrons to complete its octet of electrons. Superoxides are more reactive than peroxides, which are more reactive than oxygen, which is more reactive than an oxide.