Editing Redox (section)

===<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}}