Chemistry Reference
In-Depth Information
present, that is, electronegativity is a property of atoms arises when the atoms form
molecules. But latter, it is established that electronegativity is an intrinsic property of
a free atom [13, 14, 22, 25, 48-53].
Malone's Scale of Electronegativity [54]
Just 1 year after the announcement of the electronegativity concept by Pauling [10],
Malone [54] suggested a relationship between the dipole moment in Debye (μ
d
) of a
hetaronuclear bond X-Y and the electronegativity difference, χ
X
~ χ
Y
, as:
χ
X
~ χ
Y
μ μ
d
(3)
A deeper study on the Malone's Scale reveals that the scale can be applied remark-
ably well in a few well known cases (e.g., hydrogen halides) but in case of a majority
of compounds due to the inaccuracy in the computed result this scale cannot be ac-
cepted as a reasonable scale of electronegativity.
Mulliken's Scale of Electronegativity [55]
In 1934, an empirical spectroscopic definition of electronegativity was proposed by
Mulliken [55] as the average of the
IP
and
EA
for the valence state of an atom.
Mulliken considered two limiting resonance structures of the diatomic complex
XY.
X
∂+
Y
∂-
↔ XY ↔ X
∂-
Y
∂+
(4)
If one replaces the limiting structures by the equivalent ionic components then
equation (4) looks like:
X
+
+ Y
-
↔ X + Y ↔ X
-
+ Y
+
(5)
Case-1: Y is more electronegative than X, Y holds more negative charge than X
that is:
X + Y → X
+
+ Y
-
(6)
Energy change associated with the reaction (6) is given by the difference between
the energy required to remove an electron from A, its ionization potential (
IP
), and the
energy consumed to attach the electron to the outer shell of B, its electron affi nity (
EA
)
∆ E
(X
+
Y
-
)
=
IP
X
-
EA
Y
(7)
Case-2: X is more electronegative than Y, X holds more negative charge than Y
that is,
X + Y → X
-
+ Y
+
(8)
The consumed energy is
∆ E
(X
-
Y
+
)
=
IP
Y
-
EA
X
(9)
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