Editing Redox (section)

==Terminology==
"Redox" is a [[portmanteau]] of the words "REDuction" and "OXidation." The term "redox" was first used in 1928.<ref>{{OEtymD|redox}}</ref>

Oxidation is a process in which a substance loses electrons. Reduction is a process in which a substance gains electrons.

The processes of oxidation and reduction occur simultaneously and cannot occur independently.<ref name="gale" /> In redox processes, the reductant transfers electrons to the oxidant. Thus, in the reaction, the reductant or [[reducing agent]] loses electrons and is oxidized, and the oxidant or [[oxidizing agent]] gains electrons and is reduced. The pair of an oxidizing and reducing agent that is involved in a particular reaction is called a redox pair. A redox couple is a reducing species and its corresponding oxidizing form,<ref>{{cite journal |journal= Pure and Applied Chemistry |volume= 92 |issue= 4 |title= Terminology of electrochemical methods of analysis (IUPAC Recommendations 2019) |first1= José M. |last1= Pingarrón |first2= Ján |last2= Labuda |first3= Jiří |last3= Barek |first4= Christopher M. A. |last4= Brett |first5= Maria Filomena |last5= Camões |first6= Miroslav |last6= Fojta |first7= D. Brynn |last7= Hibbert |year= 2020 |pages= 641–694 |doi= 10.1515/pac-2018-0109 |doi-access= free }}</ref> e.g., {{chem|link=Iron|Fe|2+}}/ {{chem|link=Iron|Fe|3+}}.The oxidation alone and the reduction alone are each called a ''[[half-reaction]]'' because two half-reactions always occur together to form a whole reaction.<ref name="gale" />

In [[Electrochemistry|electrochemical reactions]] the oxidation and reduction processes do occur simultaneously but are separated in space.

===Oxidants===
{{Main|Oxidizing agent}}

Oxidation originally implied a reaction with oxygen to form an oxide. Later, the term was expanded to encompass [[Chemical substance|substance]]s that accomplished chemical reactions similar to those of oxygen. Ultimately, the meaning was generalized to include all processes involving the loss of electrons or the increase in the oxidation state of a chemical species.<ref name="Petrucci2017">{{cite book |last1=Petrucci |first1=Ralph H. |last2=Harwood |first2=William S. |last3=Herring |first3=F. Geoffrey|title=General Chemistry: Principles and Modern applications |date=2017 |location=Toronto |isbn=978-0-13-293128-1 |edition=11th |publisher=Pearson }}</ref>{{rp|A49}} Substances that have the ability to oxidize other substances (cause them to lose electrons) are said to be oxidative or oxidizing, and are known as [[oxidizing agent]]s, oxidants, or oxidizers. The oxidant removes electrons from another substance, and is thus itself reduced.<ref name="Petrucci2017" />{{rp|A50}} Because it "accepts" electrons, the oxidizing agent is also called an [[electron acceptor]]. Oxidants are usually chemical substances with elements in high oxidation states<ref name="Petrucci2002" />{{rp|159}} (e.g., {{chem|link=dinitrogen tetroxide|N|2|O|4}}, {{chem|link=permanganate|MnO|4|-}}, {{chem|link=chromium trioxide|CrO|3}}, {{chem|link=dichromate|Cr|2|O|7|2-}}, {{chem|link=Osmium(VIII) oxide|OsO|4}}), or else highly [[electronegativity|electronegative]] elements (e.g. [[Oxygen|O<sub>2</sub>]], [[Fluorine|F<sub>2</sub>]], [[Chlorine|Cl<sub>2</sub>]], [[Bromine|Br<sub>2</sub>]], [[Iodine|I<sub>2</sub>]]) that can gain extra electrons by oxidizing another substance.<ref name="Petrucci2002" />{{rp|909}}

Oxidizers are oxidants, but the term is mainly reserved for sources of oxygen, particularly in the context of explosions. [[Nitric acid]] is a strong oxidizer.<ref>{{cite web |title=Nitric Acid Fact Sheet |url=https://essr.umd.edu/sites/default/files/2021-10/NitricAcidFactSheet.pdf |website=Department of Environmental Safety, Sustainability & Risk |publisher=University of Maryland |access-date=12 February 2024}}</ref>

<div>[[File:GHS-pictogram-rondflam.svg|thumb|upright|The [[Globally Harmonized System of Classification and Labeling of Chemicals|international]] [[GHS hazard pictograms|pictogram]] for oxidizing chemicals]]</div>

===<span class="anchor" id="reducing equivalent"></span>Reductants===
{{Main|Reducing agent}}
Substances that have the ability to reduce other substances (cause them to gain electrons) are said to be reductive or reducing and are known as [[reducing agent]]s, reductants, or reducers. The reductant transfers electrons to another substance and is thus itself oxidized.<ref name=Petrucci2002/>{{rp|159}} Because it donates electrons, the reducing agent is also called an [[electron donor]]. Electron donors can also form [[charge transfer complex]]es with electron acceptors. The word reduction originally referred to the loss in weight upon heating a metallic [[ore]] such as a [[metal oxide]] to extract the metal. In other words, ore was "reduced" to metal.<ref name=Whitten>{{cite book |last1=Whitten |first1=Kenneth W. |last2=Gailey |first2=Kenneth D. |last3=Davis |first3=Raymond E. |title=General Chemistry |date=1992 |publisher=Saunders College Publishin |isbn=0-03-072373-6 |page=147 |edition=4th}}</ref> [[Antoine Lavoisier]] demonstrated that this loss of weight was due to the loss of oxygen as a gas. Later, scientists realized that the metal atom gains electrons in this process. The meaning of reduction then became generalized to include all processes involving a gain of electrons.<ref name=Whitten/> Reducing equivalent refers to [[chemical species]] which transfer the equivalent of one [[electron]] in redox reactions. The term is common in [[biochemistry]].<ref>{{Cite book| vauthors = Jain JL | title = Fundamentals of Biochemistry | publisher = S. Chand  | year = 2004 | isbn = 81-219-2453-7 }}</ref> A reducing equivalent can be an electron or a hydrogen atom as a [[Hydrogen anion|hydride ion]].<ref name="Lehninger-2017">{{Cite book|title=Lehninger Principles of Biochemistry | first1 = Albert L | last1 = Lehninger | first2 = David L | last2 = Nelson | first3 = Michael M | last3 = Cox | name-list-style = vanc |isbn=9781464126116|edition=Seventh|location=New York, NY|oclc=986827885|date = 2017-01-01}}</ref>

Reductants in chemistry are very diverse. [[Electropositive]] elemental [[metal]]s, such as [[lithium]], [[sodium]], [[magnesium]], [[iron]], [[zinc]], and [[aluminium]], are good reducing agents. These metals donate electrons relatively readily.<ref>{{cite web | url=https://chemed.chem.purdue.edu/genchem/topicreview/bp/ch19/oxred_3.php#top | title=Oxidizing and Reducing Agents }}</ref>

[[Hydride transfer reagents]], such as [[sodium borohydride|NaBH<sub>4</sub>]] and [[lithium aluminium hydride|LiAlH<sub>4</sub>]], reduce by atom transfer: they transfer the equivalent of hydride or H<sup>−</sup>. These reagents are widely used in the reduction of [[carbonyl]] compounds to [[alcohols]].<ref>{{cite book|last=Hudlický|first=Miloš|title=Reductions in Organic Chemistry |publisher=American Chemical Society |year=1996|location=Washington, D.C.|pages=429|isbn=978-0-8412-3344-7}}</ref><ref>{{cite book|last=Hudlický|first=Miloš|title=Oxidations in Organic Chemistry|publisher=American Chemical Society|year=1990|location=Washington, D.C.|pages=[https://archive.org/details/oxidationsinorga00hudl/page/456 456]|isbn=978-0-8412-1780-5|url-access=registration|url=https://archive.org/details/oxidationsinorga00hudl/page/456}}</ref>  A related method of reduction involves the use of hydrogen gas (H<sub>2</sub>) as sources of H atoms.<ref name=Petrucci2002/>{{rp|288}}