An electron acceptor is a chemical entity that accepts
electron
The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary partic ...
s transferred to it from another compound. It is an
oxidizing agent that, by virtue of its accepting electrons, is itself
reduced in the process. Electron acceptors are sometimes mistakenly called electron receptors.
Typical oxidizing agents undergo permanent chemical alteration through
covalent or
ionic reaction chemistry, resulting in the complete and irreversible transfer of one or more electrons. In many chemical circumstances, however, the transfer of electronic charge from an
electron donor may be only fractional, meaning an electron is not completely transferred, but results in an electron resonance between the donor and acceptor. This leads to the formation of
charge transfer complexes in which the components largely retain their chemical identities.
The electron accepting power of an acceptor molecule is measured by its
electron affinity
The electron affinity (''E''ea) of an atom or molecule is defined as the amount of energy released when an electron attaches to a neutral atom or molecule in the gaseous state to form an anion.
::X(g) + e− → X−(g) + energy
Note that this is ...
which is the energy released when filling the lowest unoccupied
molecular orbital (LUMO).
The energy required to remove one electron from the electron donor is its
ionization energy (I). The energy liberated by attachment of an electron to the electron acceptor is the negative of its
electron affinity
The electron affinity (''E''ea) of an atom or molecule is defined as the amount of energy released when an electron attaches to a neutral atom or molecule in the gaseous state to form an anion.
::X(g) + e− → X−(g) + energy
Note that this is ...
(A). The overall system energy change (ΔE) for the charge transfer is then
. For an exothermic reaction, the energy liberated is of interest and is equal to
.
In
chemistry, a class of electron acceptors that acquire not just one, but a set of two paired electrons that form a
covalent bond with an electron donor molecule, is known as a
Lewis acid. This phenomenon gives rise to the wide field of Lewis acid-base chemistry.
The driving forces for electron donor and acceptor behavior in chemistry is based on the concepts of
electropositivity (for donors) and
electronegativity (for acceptors) of atomic or molecular entities.
Examples
Examples of electron acceptors include
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...
,
nitrate,
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
(III),
manganese
Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy u ...
(IV),
sulfate,
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
, or in some
microorganisms the
chlorinated solvents such as
tetrachloroethylene (PCE),
trichloroethylene (TCE),
dichloroethene (DCE), and
vinyl chloride (VC). These reactions are of interest not only because they allow organisms to obtain energy, but also because they are involved in the natural
biodegradation of organic contaminants. When clean-up professionals use monitored natural attenuation to clean up contaminated sites, biodegradation is one of the major contributing processes.
In
biology
Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditar ...
, a ''terminal electron acceptor'' refers to either the last compound to receive an electron in an
electron transport chain
An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couple ...
, such as oxygen during
cellular respiration
Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...
, or the last cofactor to receive an electron within the electron transfer domain of a
reaction center during
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
. All organisms obtain energy by transferring electrons from an electron donor to an electron acceptor. During this process the electron acceptor is reduced and the electron donor is
oxidized.
See also
*
Acceptor (semiconductors)
*
Redox reactions
*
Semiconductor
References
{{Reflist
External links
Electron acceptor definition at United States Geological Survey website
Electrochemical concepts