Compounds of Oxygen - Other Inorganic Compounds

Other Inorganic Compounds

The rest of the Earth's crust is formed also of oxygen compounds, most importantly calcium carbonate (in limestone) and silicates (in feldspars). Water-soluble silicates in the form of Na₄SiO₄, Na₂SiO₃, and Na₂Si₂O₅ are used as detergents and adhesives.

Peroxides retain some of oxygen's original molecular structure (<(−O-O−). White or light yellow sodium peroxide (Na₂O₂) is formed when metallic sodium is burned in oxygen. Each oxygen atom in its peroxide ion may have a full octet of 4 pairs of electrons. Superoxides are a class of compounds that are very similar to peroxides, but with just one unpaired electron for each pair of oxygen atoms (O−
2). These compounds form by oxidation of alkali metals with larger ionic radii (K, Rb, Cs). For example, potassium superoxide (KO₂) is an orange-yellow solid formed when potassium reacts with oxygen.

Hydrogen peroxide (H₂O₂) can be produced by passing a volume of 96% to 98% hydrogen and 2 to 4% oxygen through an electric discharge. A more commercially-viable method is to allow autoxidation of an organic intermediate, 2-ethylanthrahydroquinone dissolved in an organic solvent, to oxidize to H₂O₂ and 2-ethylanthraquinone. The 2-ethylanthraquinone is then reduced and recycled back into the process.

When dissolved in water, many metallic oxide form alkaline solutions, while many oxides of nonmetals form acidic solutions. For example, sodium oxide in solution forms the strong base sodium hydroxide, while phosphorus pentoxide in solution forms phosphoric acid.

Oxygenated anions such as chlorates (ClO−
3), perchlorates (ClO−
4), chromates (CrO2−
4), dichromates (Cr₂O2−
7), permanganates (MnO−
4), and nitrates (NO−
3) are strong oxidizing agents. Oxygen forms heteropoly acids and polyoxometalate ions with tungsten, molybdenum and some other transition metals, such as phosphotungstic acid (H₃PW₁₂O₄₀) and octadecamolybdophosphoric acid (H₆P₂Mo₁₈O₆₂).

One unexpected oxygen compound is dioxygenyl hexafluoroplatinate, O+
2PtF−
6, discovered in studying the properties of platinum hexafluoride (PtF₆). A change in color when this compound was exposed to atmospheric air suggested that dioxygen was being oxidized (in turn the difficulty of oxidizing oxygen led to the hypothesis that xenon might be oxidized by PtF₆, resulting in discovery of the first xenon compound xenon hexafluoroplatinate Xe+PtF−
6). The cations of oxygen are formed only in the presence of stronger oxidants than oxygen, which limits them to the action of fluorine and certain fluorine compounds. Simple oxygen fluorides are known.