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::X- → X + e- An equivalent definition is the energy released (''E''initial − ''E''final) when an electron is attached to a neutral atom or molecule. It should be noted that the . 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 ''E''ea, meaning they would repel electrons. This is not recognized by modern chemists. The electron affinity of the noble gasses 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 smaller ''E''ea. Chlorine most strongly attracts extra electrons; Mercury most weakly attracts an extra electron. ''E''ea of noble gases are close to 0. Although ''E''ea vary in a chaotic manner across the table, some patterns emerge. Generally, Nonmetals have more positive ''E''ea than Metal s. VALUES FOR THE ELEMENTS See Also: Electron affinity (data page) The following data are quoted in KJ/mole . Elements marked with an asterisk are expected to have electron affinities close to zero on quantum mechanical grounds. PERIODIC TRENDS ''E''ea increases across a period (row) (since the radius slightly decreases, because of the increased attraction from the nucleus, and the number of electrons in the top shell increases, helping the atom reach maximum stability) in the periodic table and decrease going down a group (family) (because of a large increase in radius and number of electrons that decrease the stability of the atom, repulsing each other). MOLECULAR ELECTRON AFFINITIES ''E''ea is not limited to the elements but also applies to molecules. For instance the electron affinity for , 2006, 758 - 760 Abstract . SEE ALSO REFERENCES EXTERNAL LINKS
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