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.