Oxide

<h2 id="stoichiometry">Stoichiometry</h2>
Oxides are extraordinarily diverse in terms of <a href="/facts/Stoichiometries/I5p9cJzV">stoichiometries</a> (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 is <a href="/facts/Carbon_monoxide/CKuLtEMJ">carbon monoxide</a> and <a href="/facts/Carbon_dioxide/xGzpppEp">carbon dioxide</a>.<a class="footnote-ref" id="fnref:3" href="#fn:3">3</a> This applies to binary 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). <a href="/facts/Iron_silicate/UaPIeQRs">Iron silicate</a>, Fe2SiO4, the mineral <a href="/facts/Fayalite/UaPIeQRs">fayalite</a>, is one of many examples of a ternary oxide. For many metal oxides, the possibilities of polymorphism and nonstoichiometry exist as well.<a class="footnote-ref" id="fnref:4" href="#fn:4">4</a> 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.<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a>
For simplicity sake, most of this article focuses on binary oxides.

<h2 id="formation">Formation</h2>
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.

<h3>Metal oxides</h3>
Many metal oxides arise by decomposition of other metal compounds, e.g. <a href="/facts/Carbonate/FES1QHkN">carbonates</a>, <a href="/facts/Hydroxide/zW0wxpWD">hydroxides</a>, and <a href="/facts/Nitrate/5AnVlYnL">nitrates</a>. In the making of <a href="/facts/Calcium_oxide/Wh9C8l7j">calcium oxide</a>, <a href="/facts/Calcium_carbonate/UQ1wLFna">calcium carbonate</a> (<a href="/facts/Limestone/8ntvtFnR">limestone</a>) breaks down upon heating, releasing carbon dioxide:<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a>

CaCO
            
              3
            
            
              
            
          
          ⟶
          CaO
          +
          
            CO
            
              2
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {CaCO3 -> CaO + CO2}}}

The reaction of elements with oxygen in air is a key step in <a href="/facts/Corrosion/lIC7H4we">corrosion</a> 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 give <a href="/facts/Zinc_oxide/P7sTyDez">zinc oxide</a>:<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a>

2
          
          Zn
          +
          
            O
            
              2
            
            
              
            
          
          ⟶
          2
          
          ZnO
        
      
    
    {\displaystyle {\ce {2 Zn + O2 -> 2 ZnO}}}

The production of metals from ores often involves the production of oxides by roasting (heating) metal sulfide minerals in air. In this way, MoS2 (<a href="/facts/Molybdenite/jatlEkxR">molybdenite</a>) is converted to <a href="/facts/Molybdenum_trioxide/4QpFEqmg">molybdenum trioxide</a>, the precursor to virtually all molybdenum compounds:<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a>

2
          
          
            MoS
            
              2
            
            
              
            
          
          +
          7
          
          
            O
            
              2
            
            
              
            
          
          ⟶
          2
          
          
            MoO
            
              3
            
            
              
            
          
          +
          4
          
          
            SO
            
              2
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {2 MoS2 + 7 O2 -> 2MoO3 + 4 SO2}}}

<a href="/facts/Noble_metal/Pe9EKIvU">Noble metals</a> (such as <a href="/facts/Gold/1znknojp">gold</a> and <a href="/facts/Platinum/qJC6lQf7">platinum</a>) are prized because they resist direct chemical combination with oxygen.<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a>

<h3>Non-metal oxides</h3>
Important and prevalent nonmetal oxides are <a href="/facts/Carbon_dioxide/xGzpppEp">carbon dioxide</a> and <a href="/facts/Carbon_monoxide/CKuLtEMJ">carbon monoxide</a>. These species form upon full or partial oxidation of carbon or hydrocarbons. With a deficiency of oxygen, the monoxide is produced:<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a>

2
          
          
            CH
            
              4
            
            
              
            
          
          +
          3
          
          
            O
            
              2
            
            
              
            
          
          ⟶
          2
          
          CO
          +
          4
          
          
            H
            
              2
            
            
              
            
          
          O
        
      
    
    {\displaystyle {\ce {2 CH4 + 3 O2 -> 2 CO + 4 H2O}}}

2
          
          C
          +
          
            O
            
              2
            
            
              
            
          
          ⟶
          2
          
          CO
        
      
    
    {\displaystyle {\ce {2 C + O2 -> 2 CO}}}

With excess oxygen, the dioxide is the product, the pathway proceeds by the intermediacy of carbon monoxide:

CH
            
              4
            
            
              
            
          
          +
          2
          
          
            O
            
              2
            
            
              
            
          
          ⟶
          
            CO
            
              2
            
            
              
            
          
          +
          2
          
          
            H
            
              2
            
            
              
            
          
          O
        
      
    
    {\displaystyle {\ce {CH4 + 2 O2 -> CO2 + 2 H2O}}}

C
          +
          
            O
            
              2
            
            
              
            
          
          ⟶
          
            CO
            
              2
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {C + O2 -> CO2}}}

Elemental nitrogen (N2) is difficult to convert to oxides, but the combustion of ammonia gives <a href="/facts/Nitric_oxide/UvhdvDzp">nitric oxide</a>, which further reacts with oxygen:

4
          
          
            NH
            
              3
            
            
              
            
          
          +
          5
          
          
            O
            
              2
            
            
              
            
          
          ⟶
          4
          
          NO
          +
          6
          
          
            H
            
              2
            
            
              
            
          
          O
        
      
    
    {\displaystyle {\ce {4 NH3 + 5 O2 -> 4 NO + 6 H2O}}}

2
          
          NO
          +
          
            O
            
              2
            
            
              
            
          
          ⟶
          2
          
          
            NO
            
              2
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {2 NO + O2 -> 2 NO2}}}

These reactions are practiced in the production of <a href="/facts/Nitric_acid/UDbwGp6s">nitric acid</a>, a commodity chemical.<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a>
The chemical produced on the largest scale industrially is <a href="/facts/Sulfuric_acid/Wom6fymJ">sulfuric acid</a>. It is produced by the oxidation of sulfur to <a href="/facts/Sulfur_dioxide/jDK1fIDs">sulfur dioxide</a>, which is separately oxidized to <a href="/facts/Sulfur_trioxide/Ijvm08Lq">sulfur trioxide</a>:<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a>

S
          +
          
            O
            
              2
            
            
              
            
          
          ⟶
          
            SO
            
              2
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {S + O2 -> SO2}}}

2
          
          
            SO
            
              2
            
            
              
            
          
          +
          
            O
            
              2
            
            
              
            
          
          ⟶
          2
          
          
            SO
            
              3
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {2 SO2 + O2 -> 2 SO3}}}

Finally the trioxide is converted to sulfuric acid by a <a href="/facts/Hydration_reaction/T1Vb2u1d">hydration reaction</a>:

SO
            
              3
            
            
              
            
          
          +
          
            H
            
              2
            
            
              
            
          
          O
          ⟶
          
            H
            
              2
            
            
              
            
          
          
            SO
            
              4
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {SO3 + H2O -> H2SO4}}}

<h2 id="structure">Structure</h2>
Oxides have a range of structures, from individual molecules to <a href="/facts/Polymer/eF32E50K">polymeric</a> and <a href="/facts/Crystalline/e2R2mk3E">crystalline</a> structures. At standard conditions, oxides may range from solids to gases. Solid oxides of metals usually have polymeric structures at ambient conditions.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a> 

<h3>Molecular oxides</h3>

Although most metal oxides are crystalline solids, many non-metal oxides are molecules. Examples of molecular oxides are <a href="/facts/Carbon_dioxide/xGzpppEp">carbon dioxide</a> and <a href="/facts/Carbon_monoxide/CKuLtEMJ">carbon monoxide</a>. All simple oxides of nitrogen are molecular, e.g., <a href="/facts/Nitric_oxide/UvhdvDzp">NO</a>, <a href="/facts/Nitrous_oxide/Jvys91lI">N2O</a>, <a href="/facts/Nitrogen_dioxide/FoLvApPI">NO2</a> and <a href="/facts/Dinitrogen_tetroxide/01WfnHJh">N2O4</a>. <a href="/facts/Phosphorus_pentoxide/GKTSUNqS">Phosphorus pentoxide</a> is a more complex molecular oxide with a deceptive name, the real formula being P4O10. Tetroxides are rare, with a few more common examples being <a href="/facts/Ruthenium_tetroxide/tEpyQYR5">ruthenium tetroxide</a>, <a href="/facts/Osmium_tetroxide/cxmYVnFK">osmium tetroxide</a>, and <a href="/facts/Xenon_tetroxide/4dmHIbue">xenon tetroxide</a>.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a>

<h2 id="reactions">Reactions</h2>
<h3>Reduction</h3>
See also: <a href="/facts/Carbothermic_reduction/gj0GA25m">Carbothermic reduction</a>
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 (<a href="/facts/Thermal_decomposition/Qqx9RqkW">thermal decomposition</a>). For example, <a href="/facts/Silver_oxide/XPGcRQ2E">silver oxide</a> decomposes at 200 °C:<a class="footnote-ref" id="fnref:15" href="#fn:15">15</a>

2
          
          
            Ag
            
              2
            
            
              
            
          
          O
          ⟶
          4
          
          Ag
          +
          
            O
            
              2
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {2 Ag2O -> 4 Ag + O2}}}

Most often, however, metal oxides are reduced by a chemical reagent. A common and cheap reducing agent is carbon in the form of <a href="/facts/Coke_(fuel)/vD8xjd0m">coke</a>. The most prominent example is that of <a href="/facts/Iron/QK1JYy8E">iron ore smelting</a>. Many reactions are involved, but the simplified equation is usually shown as:<a class="footnote-ref" id="fnref:16" href="#fn:16">16</a>

2
          
          
            Fe
            
              2
            
            
              
            
          
          
            O
            
              3
            
            
              
            
          
          +
          3
          
          C
          ⟶
          4
          
          Fe
          +
          3
          
          
            CO
            
              2
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {2 Fe2O3 + 3 C -> 4 Fe + 3 CO2}}}

Some <a href="/facts/Metal_oxide/DXtoVe1C">metal oxides</a> dissolve in the presence of reducing agents, which can include organic compounds. Reductive dissolution of <a href="/facts/Ferric_Oxide/vam0XoC5">ferric oxides</a> is integral to <a href="/facts/Geochemical/05094gDu">geochemical</a> phenomena such as the <a href="/facts/Iron_cycle/xDhevRaI">iron cycle</a>.<a class="footnote-ref" id="fnref:17" href="#fn:17">17</a>

<h3>Hydrolysis and dissolution</h3>
Because the M-O bonds are typically strong, metal oxides tend to be insoluble in solvents, though they may be attacked by aqueous acids and bases.<a class="footnote-ref" id="fnref:18" href="#fn:18">18</a>
Dissolution of oxides often gives <a href="/facts/Oxyanion/0GuWXr6D">oxyanions</a>. Adding aqueous base to P4O10 gives various <a href="/facts/Phosphate/FDGVCxUG">phosphates</a>. Adding aqueous base to MoO3 gives <a href="/facts/Polyoxometalate/mr1AkgR5">polyoxometalates</a>. Oxycations are rarer, some examples being <a href="/facts/Nitrosonium/zmRlEu1k">nitrosonium</a> (NO+), <a href="/facts/Vanadyl/Guma1f7r">vanadyl</a> (VO2+), and <a href="/facts/Uranyl/XoqDjPHM">uranyl</a> (UO2+2). Many compounds are known with both oxides and other groups. In <a href="/facts/Organic_chemistry/djxhxaNg">organic chemistry</a>, these include <a href="/facts/Ketone/BqQXpLo4">ketones</a> and many related <a href="/facts/Carbonyl/KJ71bo3X">carbonyl</a> compounds. For the transition metals, many <a href="/facts/Oxo_ligand/CTR37kYS">oxo complexes</a> are known as well as <a href="/facts/Oxyhalide/vAppA4lU">oxyhalides</a>.<a class="footnote-ref" id="fnref:19" href="#fn:19">19</a>

<h2 id="nomenclature-and-formulas">Nomenclature and formulas</h2>
The <a href="/facts/Chemical_formula/hghUtthl">chemical formulas</a> of the oxides of the <a href="/facts/Chemical_element/0jducgWD">chemical elements</a> in their highest <a href="/facts/Oxidation_state/W53W6s6V">oxidation state</a> are predictable and are derived from the number of <a href="/facts/Valence_electron/mXPA15VP">valence electrons</a> for that element. Even the chemical formula of O4, <a href="/facts/Tetraoxygen/f8hMAHBQ">tetraoxygen</a>, is predictable as a <a href="/facts/Group_16_element/nXLGmnqL">group 16 element</a>. One exception is <a href="/facts/Copper/I8PEE8oX">copper</a>, for which the highest oxidation state oxide is <a href="/facts/Copper(II)_oxide/62mUJlpm">copper(II) oxide</a> and not <a href="/facts/Copper(I)_oxide/lVQAEWXx">copper(I) oxide</a>. Another exception is <a href="/facts/Fluoride/LpqNMzwa">fluoride</a>, which does not exist as one might expect—as F2O7—but as <a href="/facts/Oxygen_difluoride/7WF0HL33">OF2</a>.<a class="footnote-ref" id="fnref:20" href="#fn:20">20</a>

<h2 id="see-also">See also</h2>

Look up oxide in Wiktionary, the free dictionary.

<ul><li>Other oxygen ions <a href="/facts/Ozonide/o5dokpaf">ozonide</a>, O−3, <a href="/facts/Superoxide/2X2sQocn">superoxide</a>, O−2, <a href="/facts/Peroxide/VMU8y4xB">peroxide</a>, O2−2 and <a href="/facts/Dioxygenyl/EBakMwWS">dioxygenyl</a>, O+2.</li>
<li><a href="/facts/Suboxide/UnVJWcwX">Suboxide</a></li>
<li><a href="/facts/Oxohalide/vAppA4lU">Oxohalide</a></li>
<li><a href="/facts/Oxyanion/0GuWXr6D">Oxyanion</a></li>
<li><a href="/facts/Complex_oxide/WKGglfJH">Complex oxide</a></li>
<li>See Category:Oxides for a list of oxides.</li>
<li><a href="/facts/%F0%9F%9C%94/lsSKwGpn">Salt</a></li>
<li><a href="/facts/Wet_electrons/RCwVv81Q">Wet electrons</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Hein, Morris; Arena, Susan (2006). Foundations of College Chemistry (12th ed.). Wiley. ISBN 978-0-471-74153-4. <a href="978-0-471-74153-4" target="_blank">978-0-471-74153-4</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">C. N. R. Rao, B. Raveau (1995). Transition Metal Oxides. New York: VCH. ISBN 1-56081-647-3. <a href="1-56081-647-3" target="_blank">1-56081-647-3</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">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. PMID 12848580. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">Graf, Günter G. (2000). "Zinc". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a28_509. ISBN 3-527-30673-0. <a href="3-527-30673-0" target="_blank">3-527-30673-0</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">Roger F. Sebenik; et al. (2005). "Molybdenum and Molybdenum Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a16_655. ISBN 978-3527306732. <a href="978-3527306732" target="_blank">978-3527306732</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">Thiemann, Michael; Scheibler, Erich; Wiegand, Karl Wilhelm (2000). "Nitric Acid, Nitrous Acid, and Nitrogen Oxides". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a17_293. ISBN 978-3527306732. <a href="978-3527306732" target="_blank">978-3527306732</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">Müller, Hermann (2000). "Sulfuric Acid and Sulfur Trioxide". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a25_635. ISBN 3527306730. <a href="3527306730" target="_blank">3527306730</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">P.A. Cox (2010). Transition Metal Oxides. An Introduction to Their Electronic Structure and Properties. Oxford University Press. ISBN 978-0-19-958894-7. <a href="978-0-19-958894-7" target="_blank">978-0-19-958894-7</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
<li id="fn:15">"Silver oxide". <a href="http://chemister.ru/Database/properties-en.php?dbid=1&id=4098" target="_blank">http://chemister.ru/Database/properties-en.php?dbid=1&id=4098</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></li>
<li id="fn:16">Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></li>
<li id="fn:17">Cornell, R. M.; Schwertmann, U. (2003). The Iron Oxides: Structure, Properties, Reactions, Occurrences and Uses, Second Edition. p. 323. doi:10.1002/3527602097. ISBN 978-3-527-30274-1. <a href="978-3-527-30274-1" target="_blank">978-3-527-30274-1</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></li>
<li id="fn:18">Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></li>
<li id="fn:19">Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></li>
<li id="fn:20">Schultz, Emeric (2005). "Fully Exploiting the Potential of the Periodic Table through Pattern Recognition". J. Chem. Educ. 82 (11): 1649. Bibcode:2005JChEd..82.1649S. doi:10.1021/ed082p1649. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></li>
</ol>

Oxide open-in-new

Oxide