Oxides, peroxides, superoxides, suboxides and ozonides of group 1

When the group 1 metals are heated in an excess of air or in O₂, the principal products obtained depend on the metal: lithium oxide, Li₂O sodium peroxide, Na₂O₂ and the superoxides KO₂, RbO₂ and CsO₂.

The oxides Na₂O, K₂O, Rb₂O and Cs₂O can be obtained impure by using a limited air supply, but are better prepared by thermal decomposition of the peroxides or superoxides.

  The colours of the oxides vary from white to orange; Li₂O and Na₂O form white crystals while K₂O is pale yellow, Rb₂O yellow and Cs₂O orange. All the oxides are strong bases, the basicity increasing from Li₂O to Cs₂O. A peroxide of lithium can be obtained by the action of H₂O₂ on an ethanolic solution of LiOH, but it decomposes on heating.

   Sodium peroxide (widely used as an oxidizing agent) is manufactured by heating Na metal on Al trays in air; when pure, Na₂O₂ is colourless and the faint yellow colour usually observed is due to the presence of small amounts of NaO₂. The superoxides and peroxides contain the paramagnetic [O₂]^- and diamagnetic [O₂]^2- ions respectively. Superoxides have magnetic moments of ≈1.73µB consistent with one unpaired electron.

Partial oxidation of Rb and Cs at low temperatures yields suboxides such as Rb₆O, Rb₉O₂, Cs₇ O and Cs₁₁O₃. Their structures consist of octahedral units of metal ions with the oxygen residing at the centre; the octahedra are fused together by sharing faces. The formulae of the suboxides are misleading in terms of the oxidation states. Each contains M⁺‏ and O^2_ ions, and, for example, the formula of Rb₆O is better written as (Rb⁺‏)₆(O^2-).4e^-, indicating the presence of free electrons.

The alkali metal oxides, peroxides and superoxides react with water. One use of KO₂ is in breathing masks where it absorbs H₂O producing O₂ for respiration and KOH, which absorbs exhaled CO₂ .

Sodium peroxide reacts with CO₂ to give Na₂CO₃, rendering it suitable for use in air purification in confined spaces (e.g. in submarines); KO₂ acts similarly but more effectively.

   Although all the group 1 peroxides decompose on heating their thermal stabilities depend on cation size; Li₂O₂ is the least stable peroxide, while Cs₂O₂ is the most stable. The stabilities of the superoxides (with respect to decomposition to M₂O₂ and O₂) follow a similar trend.

    Ozonides,MO₃, containing the paramagnetic, bent [O₃]^- ion  are known for all the alkali metals. The salts KO₃, RbO₃ and CsO₃ can be prepared from the peroxides or superoxides by reaction with ozone, but this method  fails, or gives low yields, for LiO₃ and NaO₃. These ozonides have recently been prepared in liquid ammonia by the interaction of CsO₃ with an ion-exchange resin loaded with either Li‏⁺ or Na⁺‏ ions. The ozonides are violently explosive.

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