How do you find dipoles?
1 Answer
Are you referring to bond dipole moments that exist between atoms of different electronegativities, or the net molecular dipole of a polar substance?
I will try to do justice to both of these.
Explanation:
To estimate the dipole moments for each bond, it is common to use electronegativity difference between the bonded atoms as a rough gauge of the dipole strength. Subtract the two values, and point the negative end of the bond dipole toward the atom of greater electronegativity. If you require something more accurate, you should be able to look up the dipole moments for a variety of bonds.
An accurate determination of molecular dipoles will require that you know the geometry of the molecule and are somewhat versed in vector addition. The net molecular dipole is determined by adding all the dipole vectors of individual bond dipoles.
In the case of a simple molecule like water, you need only add the dipoles of the two O-H bonds. This can be done in a diagram by doing a "tip-to-tail" vector addition.
In the case of 3-dimensional molecules, the task becomes rather difficult, and an estimate is adequate in most introductory Chemistry courses.
