hi!!!

So in a molecule, when there is an electronegativity difference, the more electro-ve atom pulls the electrons, tus causing a charge separation...creating a positive and negative centre

 

eg

 

CH₃-CH₂->>F

     --|-->

 

here f takes negative charge

 

However for molecules which are symmetric, dipole moment may be 0

eg trans-1,2 dichloro ethene