non-polar and polar molecules

• depending on the shape and bond angles dipoles can cancel each other out resulting in a non-polar molecule
• if dipoles reinforce each other, the molecule will have an over all dipole and be polar
• diatomic molecules will be non-polar as they have the same electronegativity
• this arrow is used to represent a dipole

  
• the polarity of the molecule is measured in its dipole moment:

  • for a diatomic molecule, it's defined as the difference in charge multiplied by the distance of separation between the charges
  • for a polyatomic, it is more complicated because the different polarities have to be taken into account as well as any lone pairs
  • the larger the number the more polar the molecule
• a dipole is said to exist when two charges of equal magnitude but opposite signs are separated by a small distance