Dipole moments percent ionic character

Having shown that the weighting coefficient (A) of the term giving the contribution of an ionic structure to the molecular wave function is related to the dipole moment of the molecule, it is logical to expect that equations could be developed that relate the ionic character of a bond to the electronegativities of the atoms. Two such equations that give the percent ionic character of the bond in terms of the electronegativities of the atoms are... 

Calculate the percent ionic character of the X-Y bond. If the bond length is 148 pm, what is the dipole moment... 

One of the reasons for the preparation of the present article were the following statements made by Kaufman, Wharton, and Klemperer which seem to require clarification SrO has the largest percent ionic character, pijer [0.97 according to Table III in Ref. 8] yet observed for any diatomic molecule (see Abstract) Yoshimine s calculation predicts [for the BeO molecule] a dipole moment of 7.29 D and 114% ionic character (p. 952). 

PROBLEM 10.1 The dipole moment of HF is /x, = 1.82 D, and the bond length is 92 pm. Calculate the percent ionic character of the H-F bond. Is HF more ionic or less ionic than HC1 (Worked Example 10.1) ... 

The dipole moment of LiH is 1.964 x 10 29C m, and the LiH distance is 159.6 pm. What is the approximate percent ionic character in LiH Hint. First calculate the dipole moment assuming 100% ionic character, with a charge at the center of each atom equal in magnitude to that of the electric charge,... 

The approximate percent ionic character equals 100% times the fraction determined by the actual dipole moment divided by the hypothetical dipole moment. 

How well can we tell the difference between an ionic bond and a polar covalent bond The only honest answer to this question is that there are probably no totally ionic bonds between discrete pairs of atoms. The evidence for this statement comes from calculations of the percent ionic character for the bonds of various binary compounds in the gas phase. These calculations are based on comparisons of the measured dipole moments for molecules of the type X—Y with the calculated dipole moments for the completely ionic case, X+Y. We performed a calculation of this type for HF in Section 13.3. The percent ionic character of a bond can be defined as... 

Molecule Bond Length (A) Dipole Moment (D) Percent Ionic Character (100S)... 

Estimate the percent ionic character of a bond from its dipole moment (Section 3.7, Problems 33-38). 

The percent ionic character of the bonds in several interhalogen molecules (as estimated from their measured dipole moments and bond lengths) are OF (11%), BrF (15%), BrCl (5.6%), ICl (5.8%), and IBr (10%). Estimate the percent ionic characters for each of these molecules, using the equation in Problem 37, and compare them with the given values. 

Over the years numerous scales of percent ionic character have been proposed for both simple molecules and solids. They may depend on some physical property, such as dipole moments or refractive indices, or be extracted from some theoretical analysis. The various scales usually agree on a rough ordering but the actual numbers vary widely. It seems to be impossible to define exactly what is meant by percent ionic character . Therefore, the numbers in the various scales have meaning only in terms of the model from which they were derived. Each scale is useful for some experimental or theoretical property, but transfer to other properties is hazardous. 

The approximate percent ionic character equals 100 percent times the fraction actual dipole moment over the hypothetical... 

If we know the distance d between two atoms, we can calculate a theoretical dipole moment on the assumption that the atoms bear a full single charge this value is /hheor 4.8d debyes. The percent ionic character of the bond can then... 

Measuring the dipole moment of a particular bond allows us to calculate the percent ionic character of that bond. As an example, let s analyze a C—Cl bond. This bond has a bond length of 1.772 X 10 cm, and an electron has a charge of 4.80 x 10 ° esu. If the bond were 100% ionic, then the dipole moment would be... 

Bond Polarity, Dipole Moment, and Percent Ionic Character... 

By comparing the actual dipole moment of a bond to what the dipole moment would be if the electron were completely transferred from one atom to the other, we can get a sense of the degree to which the electron is transferred (or the degree to which the bond is ionic). A quantity called the percent ionic character is the ratio of a bond s actual dipole moment to the dipole moment it would have if the electron were completely hans-ferred from one atom to the other, multiplied by 100% ... 

For example, suppose a diatomic molecule with a bond length of 130 pm has a dipole moment of 3.5 D. We previously calculated that separating a proton and an electron by 130 pm results in a dipole moment of 6.2 D. Therefore, the percent ionic character of the bond is 56% ... 

The HCl(g) molecule has a bond length of 127 pm and a dipole moment of 1.08 D. Without doing detailed calculations, determine the best estimate for its percent ionic character. 

---