Question

a hypothetical molecule, X-Y has a dipole moment 1.52D and a bond length of 101pm. Calculate % ionic character.

Answer 1

The calculated dipole moment is charge on electron * radius of molecule

the calculated dipole moment (calculated assuming one electron has been completely transferred from X to Y) is dependent on the bond length (interatomic spacing), not the radius.

μ100% = electron charge⋅interatomic spacing

             = (1.6*10^−19) C .1.01*10^-10m

             = 1.616e-29 = 1.616*10^-29Cm

1D = 3.33564×10⁻³⁰ Cm

[μobs] = 1.52D = 1.52 *3.33564×10⁻³⁰ cm = 5.07×10⁻³⁰ Cm

% ionic character = [μobs]/[μ100%] = 5.07*10⁻³⁰ Cm / 1.616*10^-29 = 0.31 = 31%