Electron affinity

In solid state physics, the electron affinity for a surface is defined somewhat differently (see below).

Electron capture for almost all non-noble gas atoms involves the release of energy[4] and thus is exothermic.

Confusion arises in mistaking Eea for a change in energy, ΔE, in which case the positive values listed in tables would be for an endo- not exo-thermic process.

In this case, the electron capture is an endothermic process and the relationship, Eea = −ΔE(attach) is still valid.

Equivalently, electron affinity can also be defined as the amount of energy required to detach an electron from the atom while it holds a single-excess-electron thus making the atom a negative ion,[1] i.e. the energy change for the process If the same table is employed for the forward and reverse reactions, without switching signs, care must be taken to apply the correct definition to the corresponding direction, attachment (release) or detachment (require).

The electron affinities of the noble gases have not been conclusively measured, so they may or may not have slightly negative values.

In group 18, the valence shell is full, meaning that added electrons are unstable, tending to be ejected very quickly.

For instance the electron affinity for benzene is negative, as is that of naphthalene, while those of anthracene, phenanthrene and pyrene are positive.

At nonzero temperature, and for other materials (metals, semimetals, heavily doped semiconductors), the analogy does not hold since an added electron will instead go to the Fermi level on average.

The work function is the thermodynamic work that can be obtained by reversibly and isothermally removing an electron from the material to vacuum; this thermodynamic electron goes to the Fermi level on average, not the conduction band edge:

In semiconductor physics, the primary use of the electron affinity is not actually in the analysis of semiconductor–vacuum surfaces, but rather in heuristic electron affinity rules for estimating the band bending that occurs at the interface of two materials, in particular metal–semiconductor junctions and semiconductor heterojunctions.