Calculating Percent Ionic Character from a Dipole Moment
The dipole moment of HCl is 1.11 D, and the distance between atoms is 127 pm. What is the percent ionic character of the HCl bond?
STRATEGY
If HCl were 100% ionic, a negative charge (Cl^-) would be separated from a positive charge (H^+) by 127 pm. Calculate the expected dipole moment, and compare that calculated value to the actual value.
The calculated dipole moment is
\begin{aligned}\mu & =Q \times r \\\mu & =\left(1.60 \times 10^{-19} \mathrm{C}\right)\left(127 \times 10^{-12} \mathrm{~m}\right)\left(\frac{1 \ \mathrm{D}}{3.336 \times 10^{-30} \mathrm{C} \cdot \mathrm{m}}\right)=6.09 \ \mathrm{D}\end{aligned}The observed dipole moment of 1.11 D for HCl implies that the H-Cl bond is only about 18% ionic:
\frac{1.11 \ \mathrm{D}}{6.09 \ \mathrm{D}} \times 100 \%=18.2 \%