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Electron affinity can be defined in two equivalent ways. First, as the energy that is released by adding an electron to an isolated gaseous atom. The second (reverse) definition is that electron affinity is the energy required to remove an electron from a singly charged gaseous negative ion.
In any case, the value of the electron affinity of a solid substance is very different from the chemistry and atomic physics electron affinity value for an atom of the same substance in gas phase. For example, a silicon crystal surface has electron affinity 4.05 eV, whereas an isolated silicon atom has electron affinity 1.39 eV.
The electron affinity (usually given by the symbol in solid state physics) gives the energy difference between the lower edge of the conduction band and the vacuum level of the semiconductor. The band gap (usually given the symbol E g {\displaystyle E_{\rm {g}}} ) gives the energy difference between the lower edge of the conduction band and the ...
The energy required to remove one or more electrons to make a cation is a sum of successive ionization energies; for example, the energy needed to form Mg 2+ is the ionization energy required to remove the first electron from Mg, plus the ionization energy required to remove the second electron from Mg +. Electron affinity is defined as the ...
where I is the ionization potential and A the electron affinity. This expression implies that the chemical hardness is proportional to the band gap of a chemical system, when a gap exists. The first derivative of the energy with respect to the number of electrons is equal to the chemical potential , μ , of the system,
The energy of the second-highest MO 3a 1 refers to the ion in the excited state (1a 1) 2 (2a 1) 2 (1b 2) 2 (3a 1) 1 (1b 1) 2, and so on. In this case the order of the ion electronic states corresponds to the order of the orbital energies. Excited-state ionization energies can be measured by photoelectron spectroscopy.
The outer electron is ejected from the atom, leaving a positive ion. Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells.
By inserting the energetic definitions of the ionization potential and electron affinity into the Mulliken electronegativity, it is seen that the Mulliken chemical potential is a finite difference approximation of the electronic energy with respect to the number of electrons, i.e.,