Electron affinity sign convention

Electron affinity is conventionally defined as the energy released when an electron is added to the valence shell of an atom. Unfortunately, this is in contradiction to the universal thermodynamic convention that enthalpies of exothermic reactions shall be assigned negative signs. Since it seems impossible to overthrow the election affinity convention at this late date without undue confusion, one can adopt one of two viewpoints to minimize confusion. One is to let the electron affinities of the most active nonmetals be positive, even though in thermodynamic calculations the enthalpies are negative ... 

In some books, you will see electron affinity defined with an opposite-sign convention. Those values are actually the electron-gain enthalpies (Chapter 6). 

Tables in reference sources often give electron affinities as positive values when the negative ion is more stable than the neutral atom. This convention is contrary to the sign convention for other energetic processes, which uses negative values when energy...

Note that the proton affinity (PA) has the opposite sign from the enthalpy of reaction of Eq. 9.47 Proton affinities are always listed as positive numbers despite referring to exothermic reactions (recall the same convention with electron affinities. Chapter 3) Proton affinities may be obtained in a number of ways. The simplest, and most fundamental for defining an absolute scale of proton affinities, is to use a Bom-Haber cycle of the sort ... 

Some books and reference sources adopt the opposite sign convention for electron affinity, giving it a positive value and defining it as the energy absorbed when an anion loses an electron. 

The electron affinity of an atom or ion is the counterpart of the ionisation potential. It is an intensive property, defined as the energy released when the atom in its ground state accepts an electron, i.e. the difference in energy between the ground state of E and that of E- with the sign convention that exothermic electron affinities are positive. Electron affinities, like ionisation potentials, are expressed in eV. 

The sign convention for electron affinity values follows the convention for energy changes used in Chapters 9 and 10. 

Because two different conventions have been used, there is a good deal of confusion in the chemical literature about the signs for electron affinity values. Electron affinity has been defined in many textbooks as the energy released when an electron is added to a gaseous atom. This convention requires that a positive sign be attached to an exothermic addition of an electron to an atom, which opposes normal thermodynamic conventions. Therefore, in this... 

In general, it is also possible to attach an additional electron to any atom, ion or molecule. The energy which is released when this takes place is called the electron affinity, E, of the species. It will be noted that this sign convention is opposite to the conventional one, i.e. ... 

J.C. Wheeler (1997) Journal of Chemical Education, vol. 74, p. 123 Electron affinities of the alkaline earth metals and the sign convention for electron affinity . 

The sign convention for electron affinity can often cause confusion for students. In this textbook, why have we referred to an enthalpy change for the attachment of an electron rather than to an electron affinity ... 

Students often have difficulty with the sign conventions associated with electron affinity. For most neutral atoms and for all cations, energy is evolved when an electron is added As a consequence, the sign of the A is negative. Electron affinities of some atomic elements are positive, and some are negative. 

We use the convention that Eea > 0 signifies a positive affinity for the added electron. Distinguish the electron affinity from the electron-gain enthalpy, which is negative for such an exothermic process (that is, has the opposite sign to the electron affinity, and differs very slightly in value). 

The sign convention used for electron affinity is the normal thermodynamic one in which a negative sign corresponds to an exothermic process. 

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