Oxides, Peroxides and Superoxides of Alkali Metals

A normal ionic oxide (like Na2O) contains discrete O2- ions, with no O-O bond at all; dissolving in water gives a simple basic solution (Na2O + H2O → 2NaOH), consistent with a white, high-melting ionic solid that dissociates to a strongly basic hydroxide. A peroxide (like Na2O2) contains the peroxide ion, O2²-, with a single O-O bond and all electrons paired — this makes Na2O2 DIAMAGNETIC, not paramagnetic. A superoxide (like NaO2 or KO2) contains the superoxide ion, O2^-, which has one unpaired electron in its π-antibonding orbital, making it PARAMAGNETIC. Do not mix these up: peroxide (O2²-) is diamagnetic, superoxide (O2^-) is paramagnetic — a very common exam swap.

Hydrolysing a superoxide follows the balanced pattern 2 MO2 + 2 H2O → 2 M+ + 2 OH- + H2O2 + O2: the superoxide disproportionates on contact with water, forming the metal hydroxide, hydrogen peroxide, AND oxygen gas together. This is a more complex hydrolysis than a simple peroxide (which just gives hydroxide plus H2O2, no extra O2) or a simple oxide (which just gives hydroxide, no H2O2 or O2 at all) — the superoxide additional unpaired-electron/radical-like character is exactly why its hydrolysis releases a third product, oxygen gas, that the others do not.

Fresh sodium peroxide is a yellow solid; on exposure to moist air, it absorbs both water vapour and CO2 simultaneously, forming a mixture of NaOH (from reaction with water) and Na2CO3 (from the NaOH further reacting with atmospheric CO2), which together appear white — the colour change signals this double reaction with atmospheric moisture and CO2, not a single clean product. Potassium superoxide, KO2, is put to a very practical use exploiting exactly this same kind of chemistry: it reacts directly with CO2 (4 KO2 + 2 CO2 → 2 K2CO3 + 3 O2), simultaneously absorbing the CO2 a person exhales AND releasing fresh O2 in return — making it an ideal combined CO2 scrubber and oxygen source for a sealed environment like a space capsule or a submarine, a role no simple oxide or peroxide can fill as elegantly, since it is specifically the superoxide oxidation state that allows this dual absorb-and-release behaviour.

Sodium metal is never found free in nature (it is far too reactive, always found combined in compounds) — so a statement claiming metallic sodium occurs naturally is false. Sodium peroxide (Na2O2) is diamagnetic (as established above), so a statement claiming it is paramagnetic is false. Sodium superoxide (NaO2) is genuinely paramagnetic — true. Sodium does NOT react directly with N2 gas under ordinary conditions to form Na3N (unlike lithium, which does readily form Li3N — another instance of the lithium anomaly), so a statement claiming Na3N forms this way is false. Reading this kind of composite statement question means checking each claim independently against these specific, well-defined facts, rather than assuming alkali metals all behave identically.