Chlorine most strongly attracts extra electrons mercury most weakly attracts an extra electron. Atoms whose anions are more stable than neutral atoms have a greater E ea. Generally, nonmetals have more positive E ea than metals. Main article: Electron affinity (data page)Īlthough E ea varies greatly across the periodic table, some patterns emerge. E ea = ( E final − E initial) detach = ΔE(detach) = - ΔE(attach)
Since almost all detachments (require +) an amount of energy listed on the table, those detachment reactions are endothermic, or ΔE(detach) > 0. 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 energy change for the process X − → X + e − This expression does follow the convention ΔX = X(final) - X(initial) since - ΔE = - (E(final) - E(initial)) = E(initial) - E(final).Įquivalently, electron affinity can also be defined as the amount of energy required to detach an electron from a singly charged negative ion, i.e. The usual expression for calculating E ea when an electron is attached is E ea = ( E initial − E final) attach = - ΔE(attach) Negative values typically arise for the capture of a second electron, but also for the nitrogen atom. In this case, the electron capture is an endothermic process and the relationship, E ea = - ΔE(attach) is still valid. However, if the value assigned to E ea is negative, the negative sign implies a reversal of direction, and energy is required to attach an electron. The relation between the two is, E ea = - ΔE(attach).
Confusion arises in mistaking E ea for a change in energy, ΔE, in which case the positive values listed in tables would be for an endo- not exo-thermic process. It is the word, released within the definition energy released that supplies the negative sign. The positive values that are listed in tables of E ea are amounts or magnitudes.
Electron capture for almost all non- noble gas atoms involves the release of energy and thus are exothermic. For any reaction that releases energy, the change in energy, ΔE, has a negative value and the reaction is called an exothermic process. To use electron affinities properly, it is essential to keep track of sign. In solids, the electron affinity is the energy difference between the vacuum energy and the conduction band minimum. Together they may undergo charge-transfer reactions. Another example, a molecule or atom that has a more positive value of electron affinity than another is often called an electron acceptor and the less positive an electron donor. Other theoretical concepts that use electron affinity include electronic chemical potential and chemical hardness. Mulliken to develop an electronegativity scale for atoms, equal to the average of the electron affinity and ionization potential. A list of the electron affinities was used by Robert S. This property is measured for atoms and molecules in the gaseous state only, since in the solid or liquid states their energy levels would be changed by contact with other atoms or molecules. The electron affinity of an atom or molecule is defined as the amount of energy released when an electron is added to a neutral atom or molecule to form a negative ion. In atoms the lowest unoccupied and highest occupied atomic orbitals correspond approximately to E C and E V, respectively. E VAC, E C, E F, E V stand for vacuum energy, conduction band minimum, fermi energy and the valence band maximum, respectively. Electron affinity E EA in a band diagram for solids.
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