Dipole Moments

[donnanguyen1d]

If there is an imbalance in formal charges, does that mean there is a dipole moment or would there only be a dipole moment is there are lone pairs on the central atom? also, what characterizes something to be the biggest dipole?

[Isaiah Little 1A 14B]

Dipole moments usually pertain to an unequal distribution of electrons in a molecule. This unequal distribution arises as a result of highly-polar bonds and asymmetry within the molecule, where the charged electrons of a molecule reside together on one end of the molecule. For instance, water has a dipole moment because the electrons tend to stay near the more-electronegative oxygen atom, and the bent shape of an H2O molecule allows the molecule itself to be asymmetrical and thus polar. If a molecule has polar bonds but is symmetrical (ex; XF6), the molecule will not have a dipole moment because electrons are evenly distributed throughout the molecule.

[Angelica Mercado 1A]

The lone pairs on the central atom don't contribute to the dipole. The dipole moment is determined by the differences in the electronegativity of the atoms, but the lone pairs on the central atom of a molecule can affect the net dipole as they can change the shape of a molecule to create dipole moments that weren't there before. Dipole moment of a molecule is the resultant of all the bond dipoles so it depends on the shape of the molecule which we can determine using VSEPR, if a molecule was straight and had two equal but oppositely charged atoms on either side of the central atom, their dipole moments would cancel out. A lone pair on the central atom would now make this molecule bent and the dipole moments would no longer cancel each other out, changing the net dipole moment.

The larger the difference in electronegativities of bonded atoms, the larger the resulting dipole moment.