Electron affinity electronegativity relationship

From what you know of the relationship between ionization energies, electron affinities, and electronegativities, would you expect the addition of some d character to a hybrid to raise or lower the electronegativity for example, will sulfur be more electronegative when hybridized spi or jp [Pg.649]

Inorganic chemistry concerns molecules of all the atoms. The electron affinities of atoms, small molecules, and radicals and their relationship with the Periodic Table, electronegativities of elements, Morse curves of diatomic anions, and the energies of ion molecule reactions and bond energies are inorganic problems we have considered. Ionic radii can be estimated using potential energy curves. 

The electron affinities of many of the molecules determined in the ECD or NIMS have been verified by half-wave reduction potentials and charge transfer complex data. These methods were developed in the 1960s but have been significantly improved. The relationship between the electronegativity and the electron affinities and ionization potentials for aromatic hydrocarbons can be used to support the Ea. The use of the ECD model and these techniques to estimate the electron affinities of aromatic hydrocarbons are illustrated for selected compounds. We will also describe the use of charge transfer complex data to obtain the electron affinities of acceptors. 

The electronegativity of hydrocarbons is half the sum of the ionization potential plus the electron affinity, the Mulliken definition of the electronegativity of atoms. In the simplest approximation the electronegativity is constant and equal to the work function of graphite. This gives the relationship ... 

Other empirical concepts have been used to consolidate data. These include the isoelectronic principle, electronegativity correlations, the relationship to absorption spectra, and the effects of single and multiple substitutions of functional groups on molecules. A similar change in the electron affinities is observed when the more electronegative nitrogen atom replaces a CH group in aromatic molecules. Statistical techniques are used to establish these correlations. Because they are empirical and require additional data for their application, the results are less certain. 

Related procedures for estimating electron affinities make use of the concept of electronegativity (EN). These use the Mulliken [33] definition of absolute electronegativity, the average of the first ionization potential and the first electron affinity, EN = (IP + EA)/2. With an estimate of the Mulliken electronegativity and the experimental value of the ionization potential, the electron affinities can be calculated. When both the electron affinity and ionization potential are measured, the relationship between the EN and experiment can be examined. This has been accomplished for aromatic hydrocarbons and will be discussed in Chapter 10. 

Mulliken found that there is a relationship between ionization potential (IP) and electron affinity (EA) and defined electronegativity x as the average of those terms ... 

In 1934, Mulliken proposed a different electronegativity scale based upon the average of the ionization potential in volts (IP X X + e ) and the electron affinity (EA X + e" X ) of the gas-phase atoms. This approach is more in character with Mulliken s MO approach since IP reflects the energy of the highest occupied molecular orbital (HOMO) while the EA has a relationship to the energy of the lowest unoccupied molecular orbital (LUMO). Not surprisingly, there has been continued debate ever since over the superiority of these two and numerous later electronegativity scales. 

The equation is valid for a given valence state. For instance, for trigonal boron compounds, a value of electronegativity can be defined for sp hybrid orbitals. Moreover, if the values of the ionization energy and electron affinity are expressed in MJ.moF , then the Mulliken electronegativity scale can be related to the Pauling scale by the relationship ... 

Plot a bar chart showing electron affinity plotted next to electronegativity. Comment on the relationship between the two atomic properties. 

The following properties of astatine have been measured or estimated (a) covalent radius (b) ionic radius (At ) (c) first ionization energy (d) electron affinity (c) electronegativity (f) standard reduction potential. Based on periodic relationships and data in Table 22.4, what values would you expect for these properties ... 

Hence, it is clear that fundamentally and operationally the physico-chemical process of protonatirMi can be linked to the above akin descriptors — the ionization process, the hardness, softness, electronegativity and electrophilicity. Recently, we (Islam et al. 2010, 2011a, b Ghosh et al. 2011a) have published good number of papers where we have discussed that the three descriptors, the electronegativity, the hardness and the electrophilicity index of atoms and molecules are fundamentally qualitative per se and operationally the same. All three represent the attraction of screened nuclei towards the electron pair/bond. Thus, we can safely and reasonably conclude that the proton affinity and the three descriptors have inverse relationship. 

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