oxide

An oxide is a chemical compound that contains at least one oxygen atom bonded to another element. In inorganic chemistry, oxides are commonly binary compounds formed from oxygen with a less electronegative element, typically with oxide ions (O2−) balanced by a positive cation. Simple oxides have formulas such as MO, M2O, or MxOy, while more complex oxides include mixed oxides and those of nonmetals such as SiO2.

Oxides are broadly classified by the nature of the element they contain and the type of bonding. Metal oxides often form ionic solids and can be basic or amphoteric, whereas many nonmetal oxides are acidic. Silicon dioxide (SiO2) is a network covalent oxide. Some oxides, such as peroxides (O2^2−) and superoxides (O2^−), are considered oxides by definition but feature O–O bonds and different chemistry from simple oxides.

Occurrence and uses are diverse. Oxides are among the most common minerals in Earth's crust, including hematite (Fe2O3), magnetite (Fe3O4), rutile (TiO2), and corundum (Al2O3). Industrially important oxides include silicon dioxide (SiO2) used in glass and ceramics; aluminum oxide (Al2O3) used as an abrasive and in refractories; calcium oxide (CaO) used in cement; titanium dioxide (TiO2) used as a white pigment; zinc oxide (ZnO) used in electronics and cosmetics; and vanadium pentoxide (V2O5) used as a catalyst. Oxides play key roles in catalysis, electronics, pigments, ceramics, and materials science.