Chemistry
Electron Affinity
Electron affinity refers to the energy change that occurs when an atom gains an electron to form a negative ion. It is a measure of an atom's ability to attract and hold onto electrons. A higher electron affinity indicates a stronger attraction for electrons, while a lower electron affinity suggests a weaker attraction.
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4 Key excerpts on "Electron Affinity"
eBook - PDFPhysical Chemistry
Understanding our Chemical World
- Paul M. S. Monk(Author)
- 2005(Publication Date)
- Wiley(Publisher)
The Electron Affinity measures the attractive force between the incoming electron and the nucleus: the stronger the attraction, the more energy there is released. The factors that affect this attraction are exactly the same as those relating to ionization CREATING FORMAL CHEMICAL BONDS 73 Table 2.9 The first electron affini- ties of the Group VII(a) elements Gas E (ea) /kJ mol −1 F 2 −348 Cl 2 −364 Br 2 −342 I 2 −314 Note: there is much disagreement in the literature about the exact values of elec- tron affinity. These values are taken from the Chemistry Data Book by Stark and Wallace. If we use a different data source, we may find slightly different numbers. The trends will be the same, whichever source we consult. −400 −300 −200 −100 0 100 0 5 10 15 20 25 Atomic number Electron Affinity / kJ mol −1 F CI He Ne Ar Figure 2.16 Graph of the electron affinities E (ea) of the first 30 elements (as y ) against atomic number (as x ) energies – nuclear charge, the distance between the nucleus and the electron, as well as the number of electrons residing between the nucleus and the outer, valence electrons. Aside We must be careful with the definition above: in many older textbooks, the Electron Affinity is defined as the energy released when an electron attaches to a neutral atom. This different definition causes E (ea) to change its sign. 74 INTRODUCING INTERACTIONS AND BONDS Why is argon gas inert? First Electron Affinity and reactivity Gases such as helium, neon and argon are so unreactive that we Krypton, xenon and radon will form a very limited number of compounds, e.g. with fluorine, but only under quite excep- tional conditions. call them the inert gases. They form no chemical compounds, and their only interactions are of the London dispersion force type. They cannot form hydrogen bonds, since they are not able to bond with hydrogen and are not electronegative.
eBook - PDF- Leo J. Malone, Theodore O. Dolter(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
We will refer to this observation in the next chapter. For now, it is important to note that a filled shell represents a very stable arrangement. Thus, the magnitude of the positive charge that a representative metal can form is limited by the number of electrons beyond a noble gas configuration. 8-5.3 Electron Affinity Atoms can also gain electrons as well as lose them. The tendency of a gaseous atom to gain an electron is termed Electron Affinity (E.A.) (affinity means “an attraction for some- thing”). This process is represented symbolically as X(g) + e - ¡ X - (g) Whereas ionization energy is always an endothermic process, Electron Affinity can also be exothermic, meaning a favorable process. In this case, energy is released as an electron is added to an orbital of an atom. The added electron will enter into an empty orbital according to Hund’s rule in the same manner as the other electrons in the subshell. TABLE 8-3 Ionization Energies (kJ/mol) ELEMENT FIRST I.E. SECOND I.E. THIRD I.E. FOURTH I.E. Na 496 4565 6912 9,540 Mg 738 1450 7732 10,550 Al 577 1816 2744 11,580 8-5 Periodic Trends 263 The larger negative values (the higher electron affinities) are found to the upper right on the periodic table. This is the direction of nonmetallic behavior. This confirms what we already knew—that the representative element nonmetals have a tendency to form anions. They do so because there are one to three vacancies in their outermost p orbitals. Table 8-4 lists the electron affinities for the second period of the table. Beryllium and neon show positive electron affinities because they each have a filled subshell (2s and 2p, respectively), and so they actually have no tendency to add an electron. Nitrogen also has a positive affinity because its 2p subshell is half-filled and somewhat stable.
eBook - PDFInorganic Chemistry
An Industrial and Environmental Perspective
- Thomas W. Swaddle(Author)
- 1997(Publication Date)
- Academic Press(Publisher)
2.7 Electronegativity and Bond Energies Electronegativity (X) was defined by Linus Pauling in 1932 as a measure of the power of an atom in a molecule to draw electrons to itself. The stressed words are necessary to distinguish electronegativity from Electron Affinity. Pauling devised an electronegativity scale on the basis of thermochemical measurements of bond energies. His definition of electronegativity, however, implies two essential components of X: an atom in a molecule may attract electrons from other atoms (a function of the negative of EA, presumably) but must also retain its own electrons against the attractions of the other atoms (a function related to IP). Accordingly, Mulliken, in 1934, proposed an alternative electronegativity scale that averaged -EA and IP: IP- EA XM = 9 (2.47) 2 Here, IP and EA refer to the atom in the appropriate valence state. En- couragingly, values of Mulliken's XM are roughly proportional to those of Pauling's X, the former being larger by a factor of about 2.8. Although nowadays electronegativity tends to be regarded as an old idea, it has received renewed interest. 31 In 1989, Allen 32 presented a fresh approach in which he redefined electronegativity as the average one-electron energy of the valence shell electrons in the free atoms. He suggested that the electronegativities of the elements so calculated are sufficiently important that they should be included graphically in the periodic table as a third dimension. Parr, Pearson, and others have considered calculated electron densities in molecules as the basis for electronegativity scales. 31-36 The key property in this approach is the electronic chemical potential #: # = (OE/ON)v (2.48) where E is the electronic energy, N is the number of electrons, and v is the external potential (due mainly to the atomic nuclei) acting on the electrons.
- A. K. Haghi(Author)
- 2011(Publication Date)
- Apple Academic Press(Publisher)
Thus, the term electronegativity and its association with an electron attracting power between atoms originated with J. J. Berzelius in 1811, and its continuous use since suggests that a true chemical entity is manifest itself. However, Berzelius’ theory failed to account for half of all possible chemical reac-tions such as endothermic associations and exothermic dissociations. Moreover, Ber-zelius’ theory could not account for increasingly complex organic molecules, and also it is incompatible with Faraday’s laws of electrolysis [1]. Pauling [10, 11] first gave the objection for the use of electrode potential as a mea-sure of electron attracting power. Then, based on thermochemical data and quantum mechanical arguments, Pauling [10, 11] defined electronegativity as “the power of an atom in a molecule to attract electron pair toward itself.” Electronegativity is a funda-mental descriptor of atoms molecules and ions which can be used in correlating a vast field of chemical knowledge and experience. Allen [13, 14] considered electronega-tivity as the configuration energy of the system and argued that electronegativity is a fundamental atomic property and is the missing third dimension to the periodic table. He further assigned electronegativity as an “ad hoc” parameter. Huheey, Keiter, and Keiter [15] opined that the concept of electronegativity is simultaneously one of the 2 Modern Trends in Chemistry and Chemical Engineering most important and difficult problems in chemistry. Frenking and Krapp [16] opined that the appearance and the significance of the concepts like the electronegativity re-sembles the “unicorns of mythical saga,” which has no physical sense but without the concept and operational significance of which chemistry becomes disordered and the long established unique order in chemico-physical world will be taken aback [17–22].
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