Time Evolution of the Electronegativity - Modern Trends in Chemistry and Chemical Engineering - page 2

most important and diffi cult problems in chemistry. Frenking and Krapp [16] opined
that the appearance and the signifi cance of the concepts like the electronegativity re-
sembles the “unicorns of mythical saga,” which has no physical sense but without the
concept and operational signifi cance of which chemistry becomes disordered and the
long established unique order in chemico-physical world will be taken aback [17-22].
Fukui [23] opined that the static and dynamic behavior of molecules can be well un-
derstood by the use of the electronegativity concept. The fundamental quantities of
inorganic, organic, and physical chemistry such as bond energy, polarity, and the in-
ductive effect can be visualized in terms of electronegativity. At present, the concept of
electronegativity is not only widely used in chemistry but also in biology, physics, and
geology [24-26]. An outstanding dependence of the superconducting transition tem-
perature on electronegativity is found for both solid elements and high-temperature
superconductors [27-29]. Electronegativity concept has also been successfully used
to correlate various spectroscopic phenomenons such as nuclear quadruple coupling
from microwave and radio wave frequency spectroscopy [30] and with the chemical
shift in nuclear magnetic resonance spectroscopy [31] and so forth. Lackner and Zweig
[32] pointed out that the electronegativity has led to the correlation of vast number of
important atomic and molecular properties and also to the qualitative understanding
of quark atoms. The concept of electronegativity has been successively used by sci-
entists to explain the geometry and properties of molecule such as superconductivity,
photocatalytic activity, magnetic property, and optical basicity [33-37]. Furthermore,
in recent years, electronegativity concept has been used to design materials [38] and
drugs [39].
The intent of this work is to try to recapitulate the time evolution of the scales and
concepts of electronegativity.
VARIOUS SCALES OF ELECTRONEGATIVITY
Innumerable works of chemists from abundance of chemical observations has filled
up the field of electronegativity. Chemists have been able to derive ingenious concepts
and scales of electronegativity that have proved their usefulness in predicting and
systematizing chemical facts. In principle, pure chemical knowledge and experience
allows a reasonable estimation of electronegativity character of atoms, yet translation
of that knowledge into some numerical indexing has been the target of innumerable
workers. As a result of these intellectual exercises, ever since the concept of electro-
negativity was presented by Pauling, the useful hypothetical or qualitative entities
like the electronegativity which were abstract semiotic representations can be consid-
ered as theoretical quantities of cognitive representations. However, scientific world
till now, believe that the final scale of electronegativity is not proposed by any one.
Electronegativity is empirical and will empirical as there is no quantum mechanical
operator for it and also electronegativity is not an experimentally measurable quantity
[17-20, 40, 41]. In this section, we reviewed some of the most important and useful
scales of electronegativity of atoms, ions, and orbitals.