Electron Affinity


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electron affinity

[i′lek‚trän ə′fin·əd·ē]
(atomic physics)
The work needed in removing an electron from a negative ion, thus restoring the neutrality of an atom or molecule.

Electron Affinity

 

the ability of some neutral atoms, molecules, and free radicals to capture additional electrons and thereby become negative ions. For each specific type of particle, this ability is measured by the quantity S, known in English simply as the electron affinity. 5 is equal to the energy difference between the neutral atom or molecule in the ground state and the ground state energy of the negative ion formed after the addition of the electron.

For most atoms, the ability to add an electron results from the atoms’ outer electron shells not being filled (see). Such atoms include H atoms and elements of Group I of the periodic table, which have one outer s electron, and also atoms of groups III, IV, V, VI, and VII, which have incomplete shells. The capture of an additional electron by Fe, Co, and Ni atoms, which in the normal state have two outer electrons, is generally believed to lead to the filling of a free position in the inner 3d shell.

The value of S has been accurately determined for only a few atoms; the data on the S of molecules and radicals are, for the most part, insufficiently reliable. The 5 of atoms can be measured directly, for example, by determining the wavelength of light λ0 corresponding to the threshold of photodetachment of an electron from the negative ion: S = hcλ0, where h is Planck’s constant and c is the speed of light. The values of S for C, O, S, I, and Cl atoms have been established by this method. The use of the surface ionization effect (the vaporization of halogen atoms from the surface of incandescent W) to measure 5 has not yet yielded accurate values of 5. The reason for this failure is that, because of the polycrystalline structure of W, the work function is not the same on different parts of the surface. When two atoms are vaporized from the same surface and become negative ions, the difference in the 5 of the two atoms can be determined with much higher accuracy. Typical values of S for atoms, in electron volts (eV), are as follows: H, 0.754; C, 1.25; 0, 1.46; S, 2.1; F, 3.37; Cl, 3.65; Br, 3.35; and 1,3.08. The values of 5 for molecules and radicals vary over a wide range. In many cases they amount to fractions of an eV. Larger values, however, are also found: NO2, > 3 eV; OH ~2 eV; and CN, <3 eV.

References in periodicals archive ?
According to the Koopmen's theorm [21] the ionization energy and electron affinity can be expressed by the following relation:
The global electron affinity can also be used in combination with ionization energy to calculate another global reactivity descriptor, the electronic chemical potential (u), which can be defined [20, 26] as follows:
Calculations using density functional theory indicate a strong dependence of a carbon supports' electron affinity on its catalytic effectiveness in the alanate systems.
Nickel, with an electron affinity of 112 kJ/mol, will not galvanically immerse on copper, so electrons need to get to nickel some other way--electroless deposition.
ECD sensitivity ranges from parts per trillion to ppb, because every species has a different electron affinity, or capacity to absorb electrons.
Therefore, while the energy of the HOMO is directly related to the ionization potential, LUMO energy is directly related to the electron affinity.
The production of highly ionized atoms involves electron affinity, not temperature.
Since diamond is a wide bondgap semiconductor that exhibits negative electron affinity, it can be used to emit electrons at room temperature.
In addition, their most favorable configurations can be linked to highest electron affinity and not to the energy of the ground state [39].
Rather, free atoms in the corona are being stripped of their electrons, as they interact with condensed matter which possesses much higher electron affinity.
The only solution rests in recognizing that the formation of highly ionized emission lines in the corona stems not from extreme temperatures, but from electron affinity [2].