Everything about The Electron Affinity totally explained
The
electron affinity,
Eea, of an
atom or
molecule is the energy required to detach an electron from a
singly charged negative ion, for example, the energy change for the process::X
- → X + e
−
An equivalent definition is the energy released (
Einitial −
Efinal) when an electron is attached to a neutral atom or molecule. It should be noted that the
sign convention for
Eea is the opposite to most
thermodynamic quantities: a positive electron affinity indicates that energy is
released on going from atom to
anion.
All elements whose EA have been measured using modern methods have a positive electron affinity, but older texts mistakenly report that some elements such as alkaline earth metals have negative
Eea, meaning they'd repel electrons. This isn't recognized by modern chemists. The electron affinity of the noble gases have not been conclusively measured, so they may or may not have slightly negative EAs. Atoms whose anions are relatively more stable than neutral atoms have a greater
Eea.
Chlorine most strongly attracts extra electrons;
mercury most weakly attracts an extra electron.
Eea of noble gases are close to 0.
Although
Eea vary in a chaotic manner across the table, some patterns emerge. Generally,
nonmetals have more positive
Eea than
metals.
Values for the elements
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.
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.
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.
Molecular electron affinities
Eea isn't limited to the elements but also applies to molecules. For instance the electron affinity for
benzene is negative, as is that of
naphthalene, while those of
anthracene,
phenanthrene and
pyrene are positive.
In silico experiments show that the electron affinity of
hexacyanobenzene surpasses that of
fullerene .
Further Information
Get more info on 'Electron Affinity'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://electron_affinity.totallyexplained.com">Electron affinity Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
