Chemistry Reference
In-Depth Information
Chapter 1
Time Evolution of the Electronegativity
Part-1: Concepts and Scales
Nazmul Islam and Chandra Chur Ghosh
INTRODUCTION
The concept of electronegativity had been a part of chemical thought for nearly about
140 years. It is opined [1] that no concept more thoroughly encompasses the fabric
of modern chemistry that that of electronegativity. Nowaday, it is established that the
electronegativity is an indispensable tool in every branch (both theoretical and experi-
mental) of chemistry, physics, engineering, and biology.
The concept of electronegativity was instigated in 1809 when Avogadro [2-4]
pointed out the similarities between the acid-base neutralization process and the elec-
trical charge neutralization process. Avogadro proposed an “oxygenicity scale” on
which elements were placed depending upon their tendency to react with other ele-
ments. Thereafter, Berzelius [5-9] fi rst coined the term “electronegativity” instead of
“oxygenicity” and formulated a “universal scale of electronegativity” of the elements.
Berzelius [5, 6] further categorized elements into two classes: (a) electronegative and
(b) electropositive. Later it was established that the electronegativity data of elements
computed using Berzelius' Scale correlate remarkably well with the electronegativity
data computed using the scale of Pauling [10, 11] which was based on thermochemi-
cal data and also the scale of Allred and Rochow [12] which was based on the force
concept. Thus, the term electronegativity and its association with an electron attracting
power between atoms originated with J. J. Berzelius in 1811, and its continuous use
since suggests that a true chemical entity is manifest itself.
However, Berzelius' theory failed to account for half of all possible chemical reac-
tions such as endothermic associations and exothermic dissociations. Moreover, Ber-
zelius' theory could not account for increasingly complex organic molecules, and also
it is incompatible with Faraday's laws of electrolysis [1].
Pauling [10, 11] fi rst gave the objection for the use of electrode potential as a mea-
sure of electron attracting power. Then, based on thermochemical data and quantum
mechanical arguments, Pauling [10, 11] defi ned electronegativity as “the power of an
atom in a molecule to attract electron pair toward itself.” Electronegativity is a funda-
mental descriptor of atoms molecules and ions which can be used in correlating a vast
fi eld of chemical knowledge and experience. Allen [13, 14] considered electronega-
tivity as the confi guration energy of the system and argued that electronegativity is a
fundamental atomic property and is the missing third dimension to the periodic table.
He further assigned electronegativity as an “ad hoc” parameter. Huheey, Keiter, and
Keiter [15] opined that the concept of electronegativity is simultaneously one of the
