Ionic character, of bonds

In Chapter 6 the element hydrogen was characterized as a family by itself. Often its chemistry distinguishes it from the rest of the periodic table. We find this is the case when we attempt to predict the ionic character of bonds to hydrogen. 

The ionization energy of the hydrogen atom, 313.6 kcal/mole, is quite close to that of fluorine, so a covalent bond between these two atoms in HF is expected. Actually the properties of HF show that the molecule has a significant electric dipole, indicating ionic character in the bond. The same is true in the O—H bonds of water and, to a lesser extent, in the N—H bonds of ammonia. The ionic character of bonds to hydro-... 

The discussion of interatomic distances is less simple for intermetallic compounds than for pure metals among the complicating factors are the partial ionic character of bonds, the transfer of electrons, with consequent changes in valency, and the preferential use of the valencies of an atom in the formation of strong bonds rather than weaker ones. These factors, which of course participate in minimizing the energy of the system, usually operate to decrease the interatomic distances. Then-effects may be illustrated by some examples. 

Comparison between Ionic Characters of Bonds Derived from Experiment and Calculated from Coupling Constants (67)... 

The amount of ionic character of a bond in a molecule must not be confused with the tendency of the molecule to ionize in a suitable solvent. The ionic character of the bond is determined by the importance of the ionic structure (A+B ) when the nuclei are at their equilibrium distance (1.275 A for HC1, for example), whereas the tendency to ionize in solution is determined by the relative stability of the actual molecules in the solution and the separated ions in the solution. It is reasonable, however, for the tendency toward ionization in solution to accompany large ionic character of bonds in general, since both result from great difference in electronegativity of the bonded atoms.4... 

Contribution of Unshared Electron Pairs to the Electric Dipole Moments of Molecules.—In the preceding chapter we discussed the dipole moments of molecules, in relation to the partial ionic character of bonds, without considering the possible contribution of unshared electron pairs. A simple treatment based on hybrid orbitals provides some justification of this procedure. 

Other factors which influence the properties of polymers can be illustrated by examining the bond energies or bond strengths and the ionic character of bonds based on Si as contrasted to similar ones based on C. 

In addition to x-ray studies and dipole moments, there are other suggested ways of estimating the ionic character of bonds, but these involve more advanced considerations and none is really satisfactory. It follows then that any quantitative relationship between electronegativity and ionic character (and there are many of them that have been proposed) must be taken with reserve. 

TABLE 3A. Partial List of Electronegativities and Percentages of Ionic Character of Bonds with Oxygen... 

Table 1 Partial list of electronegativities and percentage ionic character of bonds with oxygen.

A New Approach to the Evaluation of the Ionic Character of Bonds by Thermochemical Data... 

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