12/5/2023 0 Comments Atomic reactivity definition![]() An important development in this direction has been achieved via Sanderson’s electronegativity equalization principle (Sanderson 1971). We note preliminarly that both the chemical potential and the electronegativity satisfy the following conditions: (1) their value is the same everywhere in the system under consideration, and (2) when two systems are merged together, A and B, say, with different electronegativities \(\chi _A\) and \(\chi _B\), respectively, (or different chemical potentials), the resulting system \(C=A+B\) will be characterized by a single electronegativity \(\chi _C\).Įlectronegativity is one of the descriptors of chemical reactivity more employed to understand the nature of chemical interactions (Kaya et al. In the following, we will also discuss the equally important higher-order derivatives. 2 and using finite-difference approximation to estimate slopes, one may define the ionization energy of a given chemical species S as \(I= E(S^+ ) - E(S)\), the electron affinity of S as \(A= E(S) - E(S^- )\), and summing up the previous two equations, \(I+A = E(S^+ ) - E(S^- )\). The above definition of electronegativity was introduced by Iczkowski and Margrave ( 1961) and later discussed within the context of DFT by Parr et al. Eq. ( 18) is therefore of fundamental importance in problems of chemical reactivity, even though historically it was introduced in an ‘empirical’ way (Mulliken 1934), and has been nowadays recovered within a well-founded theoretical framework. Thus the formally exact (single-electron) version of Euler equation becomesĪccording to electronegativity, Eq. ( 18), atoms and molecules can be ranked on the basis of their ability to attract or lose electrons in the presence of atoms of another chemical species. At the core of DFT stands the electron density \(\rho (\mathbf \). However, in order to deal with molecules containing a relatively large number of electrons, as well as with solids, one can make recourse to an equally accurate theory, viz. Quantum calculations based on Schrödinger’s equation have achieved a remarkable accuracy in the study of atoms and small molecules. We will eventually emphasize the importance of the Fukui functions, and their role in determining the region of a molecule where it is more favourable to add or subtract an electron during a chemical reaction. We will start from Thomas–Fermi approximation, as a precursor of Density Functional Theory, which in turn allows a non controversial definition of elusive concepts such as the chemical potential and electronegativity. ![]() ![]() In this paper, we will review the main physical concepts and theories underlying commonly used descriptors of chemical reactions, such as hardness and softness, especially with reference to acids and bases. The local character of chemical reactivity has received more attention recently, as physical, as opposed to chemical, experimental tools have been devised to measure the coordination number in metal clusters on the atomic scale through atomic force microscopy (Berwanger et al. ![]() Indeed, Density Functional Theory (DFT) allowed to determine regularities in atomic and molecular series (Pucci and March 1982, 1986a, b), which were otherwise impossible to detect within other, albeit accurate, computational schemes, which could only be applied to individual cases. In particular, models based on quantum mechanics, and more specifically on the so-called Conceptual Density Functional Theory (CDFT), are among the most credited and suggestive ones. Existing empirical models have been therefore rationalized, and new ones have been introduced. This is due to the fact that chemical reactivity describes phenomena strongly connected with the response of a substance with respect to a specific chemical reaction. Current interest in chemical reactivity is shared by both chemists, and physicists, biologists, as well as material scientists. ![]()
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