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From Wikipedia

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 know that the electronic configuration of Cr only is [Ar] 3d5 4s1. But how about Cr2+?

Answers:[Ar]3d4 4s0 elimination of electron starts from the outermost shell

Question:Write the electron configuration for the sodium atom and for the simple ion it most commonly forms. Indicate which noble gas has the same electron configuration as the ion. I've got about 20 more of these problems and I haven't a clue how to answer them. I'm hoping somebody can explain this to me so I can figure out the rest on my own. :] Thanks!

Answers:I went to http://chemistrytable.webs.com/electronegativityconfig.htm and found that the electron configuration for sodium is: [Ne] 3s1 This is the shortcut method, and from the 3s1 you can take off one electron to make "Ne" (its closest noble gas). Na+1 (I removed one electron) Try to figure out the rest for yourself.

Question:For the given electron configurations below, enter the chemical symbol for the corresponding neutral atom, cation, or anion. [Ar] 3d2 __5+ [Ar] 3d4 __5+ I thought it was Co5+ then Cu5+ but its not? Should be easy, I'm just confused with if 4s2 / 4s1 comes into play?

Answers:I am confused too - we should be seeing 4s But we are lookiing for an element that after removing 5e-s has two valence electrons above Ar so I would go with Mn+5 and then Co+5 for the next one

Question:Also, which member of the alkali metal family most stable ion contains 36 electrons?

Answers:quite easy, just take a look at the periodic table ! let's see... the Telluride ion Te2- has 54 electrons and for the alkali is Rubidium Rb+ with 36 electrons

From Youtube

Hydronium Ion Formation Tutorial.wmv :Chemistry Videos, Formation of hydronium ion, Covalent Bond, Electronic configuration, Valency, Valence Electrons, Sharing of Electrons, coordinate Bond, Oxygen, Online Class,

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