Melting Points and Ionocovalency*

Yonghe Zhang
American Huilin Institute

 

Table 4.4 shows that for the covalent bonding, the increased covalent bonding resulting from increasing the ionicity Iav, the σ- covalency rc-1 or the spatial covalency n*rc-1 can lower the transition temperatures. The melting points decrease with increasing the covalency rc-1 and the spatial covalency n*rc-1.

However, for ionic bonding (see 4.5), the ionic compounds are characterized by very strong IC potentials holding the ions together. Increasing the ionic function I(z*,Iav) tends to increase the lattice energy of a crystal. For compounds which are predominantly ionic, increased ionic function I(z*,Iav) or covalent function C( rc-1,n*rc-1.) will result in increased melting points.

 

Table 4.4 Models and Parameters and Melting Points

Compound

Cation

z*

Iav

rc-1

n*rc-1

XIC

IC

Melt.pt[43]( ۫ C)

KF

K+

1.949

4.34

0.513

1.769

0.799

0.999

880۫

AgF

Ag+

2.874

7.58

0.747

2.875

1.271

2.147

435۫

CaCl2

Ca+2

2.807

9.005

0.576

1.987

1.053

1.617

772۫

HgCl2

Hg+2

4.49

14.82

0.694

3.008

1.672

3.118

276۫

CaCl2

Ca+2

2.807

9.005

0.576

1.987

1.053

1.617

772۫

BeCl2

Be+2

2.002

13.76

1.125

2.238

1.315

2.252

405۫

NaBr

Na+

1.777

5.14

0.636

1.838

0.853

1.13

755۫

MgBr2

Mg+2

2.637

11.33

0.733

2.119

1.184

1.933

700۫۫

AlBr3

Al+3

3.303

17.76

0.826

2.388

1.512

2.73

97.5۫

KBr

K+

1.949

4.34

0.513

1.769

0.799

0.999

730۫

CaBr2

Ca+2

2.807

9.005

0.576

1.987

1.053

1.617

765۫

CsF

Cs+

2.332

3.89

0.41

1.787

0.781

0.956

684۫

BaF2

Ba+2

3.26

7.605

0.505

2.201

1.065

1.646

1280۫

 

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

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