Electron affinity screening effect

C=C bond length alone. This represents the first time that a ir-inductive" or screening effect has been demonstrated as a factor in determining electron affinities. 

The Electron Affinity for an element depends on the atomic radius, the nuclear charge, and the screening effect of inner layers of electrons. 

An electron in an atom is attracted to the nucleus but also repelled by other electrons, hence it does not feel the full strength of the nuclear attraction. On the other hand, some atoms have positive electron affinity, i.e. attract an electron as if they possessed a net positive charge. Hence the electron shells do not completely compensate the nuclear charge Z, so that an approaching electron experiences the attraction by a certain effective nuclear charge, Z > 0. In 1930 Slater [37] suggested the following approximate solution to this problem. An electron at the radius r from the nucleus is shielded (screened) from its attraction by the electron density within the sphere of... 

One reason why an atom of fluorine has a higher electron affinity compared with an atom of bromine is the screening effect. Explain. 

The screening effect is the effect the electrons in the lower energy levels (nearer the interior of the atom) have on those in the outermost levels. They, in effect, screen the outermost electrons from the pull of the nucleus because they are like-charged. This results in lower ionization energy, lower electron affinity, and larger atoms near the bottom within a family. 

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