What is the difference between bond dipole and dipole moment?

Bond dipole relates to separation of electronic charge betweeen two atoms bonded together. If they are identical then there is no separation of charge - the electron cloud is "evenly shared" between the two atoms. In such a case there is no dipole. If, however, one atoms is very electronegative, and the other one isn't, then the electronegative atom tends to "pull" electron cloud density towards itself, accumulating a partial negative charge, and the other atom receives an unevenly low share of electron density, and a partial positive charge. This bond is then said to have a bond dipole.

Classic examples of bond dipoles are those containing the most electronegative elements, oxygen, nitrogen and halogens (H-Cl, the -OH group, -NH group).

Dipole moment is the product of the separation of the ends of a dipole and the size of the partial charges. The units are "coulomb-metre" but because bond dipole moments are generally small, they are generally measured in debye units (D). 1 debye relates to an electron and a proton separated by 0.208 Angstroms. Alternatively 1 coulomb metre is 2.9979 × #10^29# debye.