ABSTRACT
The improvement of chemistry is often based on some empirical relations between some properties, which can be measured or can be found in literature and those which one wants to investigate. This is thoroughly useful because both quantities result from the same electronic structure of the molecule under consideration. The ultimate aim of chemists, till now, is to solve the fundamental and naturally occurring phenomena. For this purpose, chemists relying upon the electronic structure of the fundamental structural construct of the universe-the atom and based upon some natural occurring phenomenon and experimental observations introduced some very important structural principles. Unfortunately, many of such things are not the things of the real world. The concepts which do not originate from a “strong” theory but clearly and vividly describe a series of relations among chemical data are called the empirical entities. They are very important for the rationalization and prediction of various physico-chemical phenomena. Because of the simplicity the empirical entities accompany our structural thinking in terms of the scientific languages. Sometimes the empirical entities can be improved on the bases of some theoretical methods. As a result, time to time new concepts have been introduced in chemistry for the explanation and prediction of several observable facts, the properties of atoms and molecules and also the reactions. The theory approaches a chemical experiment via some selective approximations and simplifications which then serve as bridge between the rigorous theory and chemical reality. In 1939, in the first edition of The Nature of the Chemical Bond, Pauling [1, 2] introduced an important fundamental descriptor of science-the electronegativity. Pauling defined electronegativity as “the power of an atom in a molecule to attract electrons to it.” Till then, attempts are made to define and quantify the hypothetical entity-–the electronegativity, but the basic tenet of Pauling-“the power of atoms to attract or retain or not to release electrons” is not yet changed. There is a maxim that when there are many treatments for a disease, none of them is completely adequate. The same idea could be applied to electronegativity in view of the many attempts to define and quantify it. Allen [1989, 3] was the first who recognize that the electronegativity concept and its scale can indeed furnish the appropriate function to reproduce the observed periodicities of experimental quantities.
