Dr. Richard F.W. BaderProfessor of positiveeast.org / positiveeast.org University / Hamilton,Ontario
You are watching: How to find percent ionic character
|TheNature of the Problem|
|5.||ElectronicBasis for the Properties of the Elements|
|7.||Ionic and CovalentBinding|
|�||Classificationof Chemical Bonds|
|�||MolecularCharge Distribution of Homonuclear Diatomic Molecules|
|�||DipoleMoments and Polar Bonds|
|Tableof Contour Values|
|1.||Arrange the following compounds in the order of the increasing polarityof their bonds:CO, HF, NaCI, O2|
|2.||Pauling introduced the idea of defining the percent ionic characterpossessed by a chemical bond. A covalent bond with equal sharing of thecharge density has 0% ionic character, and a perfect ionic bond would ofcourse have 100% ionic character. One method of estimating the percentionic character is to set it equal to the ratio of the observed dipolemoment to the value of eR, all multiplied by 100.
The value of eR is, it will be recalled, the value of the dipole momentwhen one charge is completely transferred in the formation of the bondand the resulting ions are spherical. Use this method to determine the percentionic character of the bonds in the diatomic hydrides, LiH to HF. Couldany real molecule ever exhibit 100% ionic character according to this definition?
|3.||Pauling has proposed an empirical relationship which relates the percentionic character in a bond to the electronegativity difference.
From the electronegativity values given in Table7-2, it is seen that the difference (cF- cH) is greaterthan the value (cH- cLi). Usingthe above relationship, we can calculate that the bond in HF should be59% ionic while that in LiH should be only 26% ionic. Does the estimateof the relative ionic character in HF and LiH based on the electronegativitydifference agree with that obtained by a comparison of the molecular chargedensity and density difference maps for these two molecules?