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From Wikipedia

Electron acceptor

An electron acceptor is a chemical entity that accepts electrons transferred to it from another compound. It is an oxidizing agent that, by virtue of its accepting electrons, is itself reduced in the process.

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 which is the energy released when filling the lowest unoccupied molecular orbital (LUMO).

The overall energy balance (ΔE), i.e., energy gained or lost, in an electron donor-acceptor transfer is determined by the difference between the acceptor's electron affinity (A) and the ionization potential (I) of the electron donor:

{\Delta}E=A-I\,.

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, nitrate, iron (III), manganese (IV), sulfate, carbon dioxide, 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, a terminal electron acceptor is a compound that receives or accepts an electron during cellular respiration or photosynthesis. All organisms obtain energy by transferring electrons from an electron donor to an electron acceptor. During this process (electron transport chain) the electron acceptor is reduced and the electron donor is oxidized.


Electron affinity

The Electron affinity of a molecule or atom is the energy change when an electron is added to the neutral atom to form a negative ion. This property can only be measured in an atom in gaseous state.

X + e−→ X−

The electron affinity, Eea, is defined as positive when the resulting ion has a lower energy, i.e. it is an exothermic process that releases energy:

Eea = Einitial âˆ’ Efinal

Alternately, electron affinity is often described as the amount of energy required to detach an electron from a singly chargednegative ion, i.e. the energy change for the process

X−→ X + e−

A molecule or atom that has a positive electron affinity is often called an electron acceptor and may undergo charge-transfer reactions.

Electron affinities of the elements

Although Eea varies greatly across the periodic table, some patterns emerge. Generally, nonmetals have more positive Eea than metals. Atoms whose anions are more stable than neutral atoms have a greater Eea. Chlorine most strongly attracts extra electrons; mercury most weakly attracts an extra electron. The electron affinities of the noble gases have not been conclusively measured, so they may or may not have slightly negative values.

Eea generally increases across a period (row) in the periodic table. This is caused by the filling of the valence shell of the atom; a group 7A atom releases more energy than a group 1A atom on gaining an electron because it obtains a filled valence shell and therefore is more stable.

A trend of decreasing Eea going down the groups in the periodic table would be expected. The additional electron will be entering an orbital farther away from the nucleus, and thus would experience a lesser effective nuclear charge. However, a clear counterexample to this trend can be found in group 2A, and this trend only applies to group 1A atoms. Electron affinity follows the trend of electronegativity. Fluorine (F) has a higher electron affinity than oxygen and so on.

The following data are quoted in kJ/mol. Elements marked with an asterisk are expected to have electron affinities close to zero on quantum mechanical grounds. Elements marked with a dotted box are synthetically made elements—elements not found naturally in the environment.

Molecular electron affinities

The electron affinity of molecules is a complicated function of their electronic structure. For instance the electron affinity for benzene is negative, as is that of naphthalene, while those of anthracene, phenanthrene and pyrene are positive. In silicoexperiments show that the electron affinity ofhexacyanobenzene surpasses that of fullerene.

Electron affinity of Surfaces

The electron affinity measured from a material's surface is a function of the bulk material as well as the surface condition. Often negative electron affinity is desired to obtain efficient cathodes that can supply electrons to the vacuum with little energy loss. The observed electron yield as a function of various parameters such as bias voltage or illumination conditions can be used to describe these structures with band diagrams in which the electron affinity is one parameter. For one illustration of the apparent effect of surface termination on electron emission, see Figure 3 in Marchywka Effect.



From Yahoo Answers

Question:1. At the end of the electron transport chain, the final electron acceptor is __________. a. water b. oxygen c. hydrogen d. glucose 2. A red dress appears red because the red portion of the light that strikes it __________. a. is destroyed b. is completely absorbed c. is reflected d. is changed into bond energy 3. What are the products of respiration? a. carbon dioxide and water b. glucose and oxygen c. glucose and carbon dioxide d. water and oxygen 4. What is the function of nicotinamide dinucleotide phosphate (NADP+)? a. It picks up free hydrogen ions and electrons to carry them into the cell. b. It is a molecule that adds phosphates to store energy for the cell. c. It releases energy when it is combined with oxygen. d. It is the source of electrons for photosynthesis. 5. The equation: C6H12O6 + 6O2 --> 6CO2 + 6H2O represents a summary of __________. a. photosynthesis b. anaerobic fermentation c. aerobic respiration d. the Krebs cycle

Answers:1. oxygen - hence u wrok out, produce water (sweat) 2. reflected, if absorbed, then u can't see it. 3. carbon dioxdie and water 4. this is tricky, my guess is source of electron for photosynthesis (usually its involve in the energy production pathways of an organism) 5. aerobinc respiration

Question:There are two major products of photosynthesis water and organic substances such as glucose. How would the presence of DPIP (2,6-Dichlorophenol-Indophenol, electron accepting compound) affect the production of oxygen during the light reaction? How would the presence of DPIP affect the production of organic product during the dark reaction? What role did another artificial electron acceptor, ferricyanide, play in elucidating the process of photosynthesis?

Answers:By accepting electrons, DPIP will speed up electron flow, water splitting and oxygen production. DPIP ain't NADPH so I would imagine thed dark rxn would probably be inhibited.

Question:The final electron acceptor in aerobic respiration is Oxygen, but what about anaerobic respiration?

Answers:Pyruvate! If it is anaerobic, no oxygen would be available.

Question:Indicate the final electron acceptor used in the type of metabolism you chose. I chose sulfate reduction. I can not find this anywhere. Does anyone know the anser or a website where I can research it. PLEASE HELP!!!

Answers:I can only find sulfate reduction in the metabolism of archea and bacteria in my bio book. It's biological science by scott freeman. Under sulfate reducers, it lists H2 or organic compounds as the e- donor, (SO4)2- as the e- acceptor. The by products are H2O or CO from the donor and H2S from the acceptor. Hope this helps.

From Youtube

Photosynthesis Song :Whitney and Ryan's biology project...Rap to Yeah by Usher Lyrics: Pho- pho- pho- pho-to Synthesis Pho- pho- pho- pho-to Synthesis Up in the chloroplasts tryin'a make a little ATP but it's down on the low key, Cuz you know how it is. You see I needed some photons only a length of 680, cuz that's all I absorb. Cuz of absorption spectrum. A wavelength of 680 It made the z protein ready to go (watch out, oh, watch out) It splits up water you know. H2O splits to give us oxygen to breathe, and two electrons Along with two hydrogen's. (Pho-to)--Photo system 1 accepts the sunlight (Pho-to)--Photo system 2 makes the ATP. (Pho-to)--Calvin cycle makes the sugar finally. (Synthesis)--That's how photosynthesis is done in c3's Pho- pho- pho- pho-to Synthesis Pho- pho- pho- pho-to Synthesis O2 diffuses through the thylakoids; the electrons get excited for ETC Electron transport chain Enzymes use energy from electrons; pass them along make a concentration gradient forms ATP Electrons go to photo system 2 with a new wavelength Yo! Length of 700 makes the electrons excited again, fo Ferrodoxin homes Takes them in with NAD+ and ADP + Pi Makes ATP and NADPH (Pho-to)--Photo system 1 happens in the grana (Pho-to)--Right near the openings called the stomata (Pho-to)--The whole thing is a redox reaction nana (Synthesis)--And a protein pump helps make ATP Calvin! Watch out! My process is ridiculous, in the stroma endin' photosynthesis. And rowl! CO2 is on the prowl. If it enters me, Imma make ...

The Electron Transport Chain (ETC) :An electron transport chain (ETC) couples a reaction between an electron donor (such as NADH) and an electron acceptor (such as O2) to the transfer of H+ ions across a membrane, through a set of mediating biochemical reactions. These H+ ions are used to produce adenosine triphosphate (ATP), the main energy intermediate in living organisms, as they move back across the membrane. Electron transport chains are used for extracting energy from sunlight (photosynthesis) and from redox reactions such as the oxidation of sugars (respiration). In chloroplasts, light drives the conversion of water to oxygen and NADP+ to NADPH and a transfer of H+ ions. NADPH is used as an electron donor for carbon fixation. In mitochondria, it is the conversion of oxygen to water, NADH to NAD+ and succinate to fumarate that drives the transfer of H+ ions. While some bacteria have electron transport chains similar to those in chloroplasts or mitochondria, other bacteria use different electron donors and acceptors. Both the respiratory and photosynthetic electron transport chains are major sites of premature electron leakage to oxygen, thus being major sites of superoxide production and drivers of oxidative stress. More info: Spongelab Biology: www.spongelab.com/biology