Chemical compound where oxygen atoms are combined with atoms of other elements
For negatively-charged polyatomic ion containing oxygen, seeOxyanions.
Theunit cell ofrutile, an important oxide of titanium. Ti(IV) centers are grey; oxygen centers are red. Notice that oxygen forms three bonds to titanium and titanium forms six bonds to oxygen.
Oxides are extraordinarily diverse in terms ofstoichiometries (the measurable relationship between reactants and chemical equations of an equation or reaction) and in terms of the structures of each stoichiometry. Most elements form oxides of more than one stoichiometry. A well known example iscarbon monoxide andcarbon dioxide.[2] This applies tobinary oxides, that is, compounds containing only oxide and another element. Far more common than binary oxides are oxides of more complex stoichiometries. Such complexity can arise by the introduction of other cations (a positively charged ion, i.e. one that would be attracted to the cathode in electrolysis) or other anions (a negatively charged ion).Iron silicate, Fe2SiO4, the mineralfayalite, is one of many examples of a ternary oxide. For many metal oxides, the possibilities of polymorphism and nonstoichiometry exist as well.[3] The commercially important dioxides of titanium exists in three distinct structures, for example. Many metal oxides exist in various nonstoichiometric states. Many molecular oxides exist with diverse ligands as well.[4]
For simplicity sake, most of this article focuses on binary oxides.
Oxides are associated with all elements except a few noble gases. The pathways for the formation of this diverse family of compounds are correspondingly numerous.
The reaction of elements with oxygen in air is a key step incorrosion relevant to the commercial use of iron especially. Almost all elements form oxides upon heating with oxygen atmosphere. For example, zinc powder will burn in air to givezinc oxide:[5]
The production of metals from ores often involves the production of oxides by roasting (heating) metal sulfide minerals in air. In this way,MoS2 (molybdenite) is converted tomolybdenum trioxide, the precursor to virtually all molybdenum compounds:[6]
Noble metals (such asgold andplatinum) are prized because they resist direct chemical combination with oxygen.[2]
Important and prevalent nonmetal oxides arecarbon dioxide andcarbon monoxide. These species form upon full or partial oxidation of carbon or hydrocarbons. With a deficiency of oxygen, the monoxide is produced:[2]
With excess oxygen, the dioxide is the product, the pathway proceeds by the intermediacy of carbon monoxide:
Elemental nitrogen (N2) is difficult to convert to oxides, but the combustion of ammonia givesnitric oxide, which further reacts with oxygen:
These reactions are practiced in the production ofnitric acid, a commodity chemical.[7]
The chemical produced on the largest scale industrially issulfuric acid. It is produced by the oxidation of sulfur tosulfur dioxide, which is separately oxidized tosulfur trioxide:[8]
Finally the trioxide is converted to sulfuric acid by ahydration reaction:
Oxides have a range of structures, from individual molecules topolymeric andcrystalline structures. At standard conditions, oxides may range from solids to gases. Solid oxides of metals usually have polymeric structures at ambient conditions.[9]
Reduction of metal oxide to the metal is practiced on a large scale in the production of some metals. Many metal oxides convert to metals simply by heating (thermal decomposition). For example,silver oxide decomposes at 200 °C:[10]
Most often, however, metal oxides are reduced by a chemical reagent. A common and cheap reducing agent is carbon in the form ofcoke. The most prominent example is that ofiron ore smelting. Many reactions are involved, but the simplified equation is usually shown as:[2]
^Hein, Morris; Arena, Susan (2006).Foundations of College Chemistry (12th ed.). Wiley.ISBN978-0-471-74153-4.
^abcdefghiGreenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann.ISBN0-7506-3365-4.
^C. N. R. Rao, B. Raveau (1995).Transition Metal Oxides. New York: VCH.ISBN1-56081-647-3.
^Roesky, Herbert W.; Haiduc, Ionel; Hosmane, Narayan S. (2003). "Organometallic Oxides of Main Group and Transition Elements Downsizing Inorganic Solids to Small Molecular Fragments".Chem. Rev.103 (7):2579–2596.doi:10.1021/cr020376q.PMID12848580.
^Cornell, R. M.; Schwertmann, U. (2003).The Iron Oxides: Structure, Properties, Reactions, Occurrences and Uses, Second Edition. p. 323.doi:10.1002/3527602097.ISBN978-3-527-30274-1.
