Chemistry Reference
In-Depth Information
Chapter 2
Applications
Nazmul Islam and Chandra Chur Ghosh
INTRODUCTION
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 structur-
al 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 de-
scribe 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 struc-
tural 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 electronega-
tivity concept and its scale can indeed furnish the appropriate function to reproduce the
observed periodicities of experimental quantities.
In the Part-1 of this review work, we [4] have analyzed the fact that exact defi nition
and the best method for the evaluation of electronegativity remains to be discovered.
There is plenty of room for controversy, and no two workers will agree completely.
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