Ionocovalency quantitatively explains Inert Pair Effect

Inert Pair Effect (6s2 Elements) [1]

 

Yonghe Zhang
American Huilin Institute

  

For the inert pair effect in Tl(I), Pb(II), and Bi(III), the Relativistic effects can give a qualitative verbalize: “The s orbitals of the heavier elements become more stable than otherwise expected” [39]. In IC model, the effect is attributable to the fact that the bond property in this case is controlled by the ionic function I(Iav). They are more stable in ionic compounds than in the entirely covalent form. Their IEs for forming higher covalent bonds are too much higher to form a stable hybridizing ionicity Iav:

 

Table 3.7 Atomic Parameters of Tl, Pb and Bi

Cations

Tl+

Tl2+

Tl3+

Pb2+

Pb3+

Pb4+

Bi3+

Bi4+

Bi5+

Iz

6.11

20.4

29.8

15

32

42.3

25.6

45.3

56

Iav

6.11

13.26

18.77

11.21

18.14

24.18

16.63

23.72

30.18

XIC

1.16

1.59

1.75

1.45

1.74

1.94

1.69

1.95

2.15

IC

1.89

2.92

3.31

2.58

3.44

3.78

3.16

3.81

4.27

 

[1] Zhang, Y. Ionocovalency and Applications 1. Ionocovalency Model and Orbital Hybrid Scales. Int. J. Mol. Sci. 2010, 11, 4381-4406

 

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