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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:I understand what the term "final electron acceptor" means when refered to respiration. I do not understand how fermentation can have a "final electron acceptor" without have a electron transport chain? how does the fermentation cycle work? Please help!!!!!!!!!!!

Answers:The NADH needs to be recycled, so it reduces the original carbon source, ethanol in yeast, lactic acid in humans.

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:Name all the pathways for the Aerobic Respiration, Anaerobic Respiration and Anaerobic fermentation. Also include final electron acceptors for each and products for each.

Answers:You may want to research the Periodic table for this one because that is the only place I can think of it as in. http://www.webelements.com/

Question:Question 2 Which of these consumer products are made in part by microbial fermentation? Olive oil Yogurt Beer Chocolate Soy Sauce Question 1 Which of the following can serve as a terminal electron acceptor? Methane Ethanol nitrate Oxygen Carbon dioxide Water

Answers:Yogurt, Beer, Soy Sauce. Oxygen, Nitrate, Carbon Dioxide