Electronegativities from ionization potentials

SIMS is a technique of direct mass analysis where the ion sputter is removed from the surface and, as a result of the ion bombardment, it is analyzed. By measuring both positive and negative ions, two different types of mass spectra are obtained. Positive SIMS is especially sensitive to low Z elements, which have low electronegative and ionization potential, while the negative SIMS is most sensitive to low Z elements with high electronegativity. The SIMS spectrum shown in Fig. 2.14 (Denison et al., 1988a, b) as a function of mass number is typical of that obtained from a carbon fiber surface. 

The recent interest in the exploration of electrocatalytic phenomena from first principles can be traced to the early cluster calculations of Anderson [1990] and Anderson and Debnath [1983]. These studies considered the interaction of adsorbates with model metal clusters and related the potential to the electronegativity determined as the average of the ionization potential and electron affinity—quantities that are easily obtained from molecular orbital calculations. In some iterations of this model, changes in reaction chemistry induced by the electrochemical environment... 

In our context one of the main prerequisites was a procedure for calculating atomic charges which was very rapid, as it is sometimes necessary to process many molecules of a fairly large size. The method we developed starts from the electronegativity concept, and uses electronegativity data, derived from atomic ionization potentials, IP, and electron affinities, EA (Eq. 2)36). 

Pauling based electronegativity values on bond energies between atoms, but that is not the only way to approach the problem of the ability of atoms in a molecule to attract electrons. For example, the ease of removing an electron from an atom, the ionization potential, is related to its ability to attract electrons to itself. The electron affinity also gives a measure of the ability of an atom to hold on to an electron that it has gained. These atomic properties should therefore be related to the ability of an atom in a molecule to attract electrons. Therefore, it is natural to make use of these properties in an equation... 

This is true for our procedure for calculating partial atomic charges in a-bonded molecules (16). The method starts from Mulliken s definition of electronegativity, x> derived from atomic ionization potentials, IP, and electronegativities, EA (Equation 3)(17). 

General speciation behaviors, such as those summarized in Table 5.9, can also be predicted from an element s ionization potential and electronegativity. For example, the... 

Table 1.6 Elemental properties first four ionization potentials (II, 12,13,14, from Samsonov, 1968 values expressed in eV values in parentheses are of doubtful reliability) electron affinity (e.a., from Samsonov, 1968 eV) Pauling s electronegativity (P, from Samsonov, 1968 eV) Sanderson s electronegativity (S, from Viellard, 1982 adimensional). 

Crystal radius, orbital radius, and ionization potential from Karplus and Porter (1970). Electronegativity from Pauling (1970). 

Abstract. Calculations of the first-order shell corrections of the ionization potential, 6il, electron affinity, 5 A, electronegativity, ix, and chemical hardness. Sir] are performed for elements from B to Ca, using the previously described Strutinsky averaging procedure in the frame of the extended Kohn-Sham scheme. A good agreement with the experimental results is obtained, and the discrepancies appearing are discussed in terms of the approximations made. 

In the next section we shall recall the definitions of the chemical concepts relevant to this paper in the framework of DFT. In Section 3 we briefly review Strutinsky s averaging procedure and its formulation in the extended Kohn-Sham (EKS) scheme. The following section is devoted to the presentation and discussion of our results for the residual, shell-structure part of the ionization potential, electron affinity, electronegativity, and chemical hardness for the series of atoms from B to Ca. The last section will present some conclusions. 

The property of the electronegativity of an atom in a molecule is different from the electrode potential of the element, which depends on the difference in free energjr of the element.in its standard state and in ionic solution, and it is different from the ionization potential of the atom, and from its electron affinity although it is related to these properties in a general way. 

It is generally assumed that the properties of the various families of the periodic chart change smoothly from less metallic (or more electronegative) at the top of the family to more metallic (or less electronegative) at the bottom of the family. Certainly for the extremes of the chart—the alkali metals on the left and the halogens and noble gases on the right—this Is true the ionization potentials, for example, vary in a rather monotonous way. This is not true For certain central parts of the chart, however. 

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