Chemistry Reference
In-Depth Information
1.4
1.2
1
0.8
Pauling
0.6
Mulliken
0.4
Allred-Rochow
0.2
0
Li
Na KRb s
Fr
FIGURE 3.2
The electronegativities of the elements in group 1A calculated by Pauling,
Mulliken, and Allred-Rochow methods (Mulliken values are not determined for Cs and Fr).
The chemical potential (defined below) is equal, but has an opposite sign, to the
Mulliken electronegativity,
EI
+
EA
µ=−χ =−
.
(3.7)
M
2
When electronegativity values obtained by the Allred-Rochow and Mulliken for-
mula are converted to the Pauling scale, they produce values comparable to those
from the Pauling scale (Figure 3.2).
The Sanderson method introduced a new parameter, the stability ratio, which is
calculated with the following formula (Sanderson 1955),
=
ρ
ρ
(3.8)
e
S
i
where ρ
e
is the medium electronic density, and ρ
i
represents the most stable elec-
tronic density for that respective number of electrons. The values of ρ
i
are obtained
by linear extrapolation of ρ
i
values of the preceding and succeeding noble gases for
the considered atom. For example, aluminum is found between the rare gases, neon
(ρ
i
= 1.06) and argon (ρ
i
= 0.82). If the eight supplementary electrons that appear at
the argon atom are compared with the neon atom, the density difference (Δρ
i
) is
equal to 0.24 (ρ
iNe
− ρ
iAr
). The aluminum atom, which possesses three supplementary
electrons compared to the neon atom, ρ
i
, will be calculated as
8
3
ρ=ρ−⋅ =−=
.
(3.9)
0.24
1.6
0.09
0.97
iAr
iNe
