Question

Compare the dipole moment of the following.

CH₃F,CH₃Cl,CH₃Br, CH3 I.

Answer 1

Dipole moment = Partial charge on atom * Bond length

Even though F is more electronegative, CH3Cl has greater dipole moment because the bond length in this case is far longer than that in the case of CH3F since F is highly electronegative and it attracts the electron pair very strongly. Dipole moment is not just about charge, it is the product of charge and the bond length.
Electronegativity is the determining factor for the others.

CH3Cl>CH3F>CH3Br>CH3I