Hydrogen has a lower unconventional value than Boron

Yonghe Zhang

American Huilin Institute

 

Pauling’s scale is estimated from the bond dissociation energies of two atoms, hydrogen and chlorine,and then arbitrarily extended to all elements not based on the quantitative configuration energy data [2].

Hydrogen has the lowest energy, E = -13.6 eV. Batsanov got its experimental covalent radius of 0.37 Å [3] equal to the Heitler-London’s half H-H value R (R = 0.74 Å) [4]. Based on these spectroscopic data and the IC modelEq 2.1.5, we got its IC value of 2.297eV and its electronegativity, XIC of 1.333Table 3.2.1 that is not that conventionally high as 2.2.

 

          Table 3.2.1. IC and XIC for hydrogen and the top elements

Elements

Li

Be

H

B

C

N

O

F

IC

1.023

2.064

2.297

3.291

4.302

5.329

6.273

7.37

XIC

0.808

1.237

1.333

1.743

2.167

2.583

2.972

3.423

 

The result is strongly supported by the point-charge distribution in hydrides (Table 3.2.2) proposed by Mo [5], which shows that in the typical ionic LiH (lithium monohydride) hydrogen gains point charge of 0.783, in the weak ionic BeH (beryllium monohydride) gains only 0.044, but in the covalent BH (boron monohydride) starts to loss point charge. That means that the ionocovalency and the electronegativity of hydrogen are smaller than that of boron. And moreover, the data of electric dipole moments for AlH (aluminum monohydride) (Table 3.2.3) proposed by National Institute of Standards and Technology [6]shows that the aluminum end of the dipole is negative. That means that the ionocovalency and theelectronegativity of hydrogen are smaller than that of aluminum.

 

      Table 3.2.2 Point-charge distribution qA and Dipole moment

Hydrides

LiH

BeH

BH

CH

NH

OH

FH

Bond length(expr)

1.595

1.343

1.233

1.12

1.038

0.971

0.917

Dipole moment(expr)

5.88

-

-

1.46

-

1.66

1.82

Dipole moment(calc)

5.999

0.281

-1.689

-1.647

-1.743

-1.864

-2.02

qA

0.783

0.04

-0.29

-0.31

-0.35

-0.4

-0.46

 

Table 3.2.3 Bond length and Dipole moment

 

 

 

 

Bond

H-Na

H-Mg

H-Al

H-Si

H-Se

H-P

H-S

H-Cl

Bond length(expr)

1.887

1.73

1.648

1.52

1.475

1.422

1.341

1.275

Dipole moment(cal)

5.966

1.231

-0.169

-0.332

-0.634

-0.651

-1.06

-1.468

 

Hydrogen has one valency orbital and single electron. It can be an anion to form an ionic bond by gaining another electron and it can be a cation to form a covalent bond by sharing another electron. Therefore, the IC and the XIC values of hydrogen happen to lie on the border between the weaker ionic beryllium and the weaker covalent boron (Chart 1 and Table 1). We can assign the IC value of hydrogen (2.297) as a standard to estimate the ionocovalent character of the cations. The cations with the IC values smaller than that of hydrogen we call the ionic cations and those with the IC values greater than that of hydrogen we call the covalent cations. The cations with IC values greater than that of beryllium (2.064) and smaller than that of boron (3.291) we might call borderline cations. The greater the IC than that of hydrogen, the more covalent and the less ionic the caton is, and vice versa.

 

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

[2] L. Pauling, J. Am. Chem. Soc. 54 (1932) 3570.

[3] S. S. Batsanov, Russian Chemical Bulletin, 44, 12 (1995) 2245-2250

[4] J.A. Duffy, General Inorganic Chemistry, 2nd ed., Longmans, 1974, p.19-20.

[5] Y.-R. Mo, University Chemstry, 8, 4 (1993) 15.

[6] Computational Chemistry Comparison and Benchmark DatabaseIII, E, 2, National Institute of Standards and Technology, NIST Standard Reference Database 101Release 14Sept 2006

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