The atoms in a molecule bond by sharing electrons. Theoretically, the atoms share electrons equally, so the positive electrical charge in one atom balances the negative electrical charge in another atom. In practice, however, electron sharing is imperfect, as atoms bonded to each other do not overlap perfectly. Thus, the electron carries a slight electric charge as it travels from one atom to another in a bonded pair. The charge gets bigger as the distance between the bonded atoms increases. This charge is known as a dipole moment, and the substance made up of these types of pairs is considered dipolar. Water is an example of a dipolar substance.
Things You'll Need
 Value of ionic charge in coulombs
 Distance between atoms in meters
 Pencil
 Paper
 Calculator

Write the formula for dipole moments on your paper: m = d * R. In this formula, m stands for the absolute value of the dipole moment, meaning you will express the dipole moment as a positive number, even if the actual calculation yields a negative number. "D" stands for the value of the charge, measured in coulombs. When calculating dipole moments, you may choose either the negative charge of one atom or the positive charge of the other, as they are equal. "R" stands for the distance in meters between the positive and negative ions.

Plug the numbers for "d" and "R" into the equation in the previous step, and perform the calculation. Use coulomb meters as your unit of measurement.

Convert the result into debyes, using the formula D = (3.336 1030) coulomb meters. In other words, divide the value you got in the previous step by 3.336 1030 to convert it to debyes.
References
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