Time Evolution of the Electronegativity - Modern Trends in Chemistry and Chemical Engineering - page 19

where “a” and “b” are the constants.
They evaluated the values for “a” and “b” as a = 0.105 and b = 0.863 through a lin-
ear regression of the effective ionic potential with the Pauling electronegativity data.
They calculated the electronegativities of 82 elements in different valence states
and with the most common coordination numbers using the above ansatz and found
that for a given cation, the electronegativity increases with increasing oxidation state
and decreases with increasing coordination number.
It is important here to mention that the Avogadro's Oxygenicity Scale was a crude
electronegativity scale, however, a theoretical justifi cation of Avogadro's attempt can
be made using the electrifi cation approaches [44, 96] to defi ne electronegativity.
Some important chemical phenomena, such as the ligand fi eld stabilization, the
fi rst fi lling of p orbitals, the transition-metal contraction, and especially the lanthanide
contraction, are well-refl ected in the relative values of the proposed scale of elec-
tronegativity by Li and Xue. The scale can also be used to estimate the Lewis acid
strength quantitatively for the main group elements in their highest oxidation state.
Noorizadeh and Shakerzadeh's Scale of Electronegativity [97]
Parr et al. defined the electrophilicity index, ω of atoms, ions, and molecules as
ω = μ 2 /2η= χ 2 /2η (71)
As the electrophilicity [98] of a system is related to both the resistance and the
tendency of the system to exchange electron with the environment, Noorizadeh and
Shakerzadeh [97] pointed out that the electrophilicity index can be used to measure the
electronegativity of the system.
In reference to nucleophilic-electrophilic, acid-base, or donor-acceptor reaction,
the electrophilicity index [98] of atoms and molecules seems to be an absolute and
fundamental property of such chemical species because it signifi es the energy lower-
ing process on soaking electrons from the donors. This tendency of charge soaking
and energy lowering must develop from the attraction between the soaked electron
density and screened nuclear charge of the atoms and molecules. It, therefore, tran-
spires that the conjoint action of the shell structure and the physical process of screen-
ing of nuclear charge of the atoms and molecules lead to the development of the new
electrostatic property--the electrophilicity, electronegativity, hardness of atoms and
molecules [21, 22, 40, 41].
Ghosh and Islam's Scale of Electronegativity (2009)
Ghosh and Islam [22] recently pointed out the conceptual commonality between the
two fundamental theoretical descriptors, electronegativity and hardness. They con-
cluded that the hardness and the electronegativity originate from the same source, the
electron attracting power of the screened nucleus upon valence electrons and discov-
ered the surprising result that if one measures hardness, the electronegativity is simul-
taneously measured and vice-versa.