The Time Evolution of the Electronegativity - Modern Trends in Chemistry and Chemical Engineering - page 38

to extend over an infi nite volume. The energy of this system from the equation W =
W 0 + (W 1 /R) + (W 2 /R 2 ) is W(∞) = W(0), but the W(0) value is arbitrary. The real end
product of the dissociation of a homonuclear diatomic molecule is of course two neu-
tral atoms at infi nite separation. Therefore, having the R = ∞ confi guration of the ions
and the bond charge, Pasternak then divided the bond charge and recombined it with
the ions. This involves the gain in energy by an amount W i , equal to the twice of the
energy required to removal of Z electrons from a single atom.
Thus, the energy of the system of two infi nitely separated systems of two infi nitely
separated neutral atoms is zero.

Thus, W(0) = W i (65)

The dissociation energy D is:

D = W(∞) - W i - W(R) (66)

Or, D = - W i - (W 1 /R) - (W 2 /R 2 ) (67)

Pasternak [21] established that the term W i is a continuous function of Z and can
be written as:

W i = 2(aZ + bZ 2 ) (68)

where the coeffi cients a and b are determined from the experimental ionization
energies.
Although many bond dissociation energies of chemical bonds between various
kinds of atoms in many molecules have been determined experimentally, there is at
present no reliable theoretical or empirical method for estimating bond dissociation
energies.

STABILITY RATIO
The ratio of the average electronic density of an atom to that of a hypothetical, isoelec-
tronic inert atom, is termed (Sanderson, 1952) as the “stability ratio” (SR)
The term SR is defi ned (Sanderson, 1952) as:

SR = D/D i (69)

with D = 3Z/4Пr 3 (70)

D i was defi ned as the electron density of an isoelectric inert atom, determined by
interpolation between real values, which was needed to correct the average electron
density (D) for variations in Z that were unrelated to chemical reactivity. Sanderson
[11] pointed out that the relative average electronic densities of the atoms of the ele-
ments can be used as a tool for the measurement of the electronegativity. The SR thus
can be estimated from the knowledge of electronegativity. The relation of SRs to Paul-
ing electronegativities has previously been presented graphically (Sanderson, 1952),
but the numerical dissimilarity has made diffi cult a precise quantitative comparison.