What is the difference between bond dipole and dipole moment?

The former relates qualitatively to uneven share of charge density between two bonded atoms. The latter is a quantitative measure of this.

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 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.