See explanation.
The structures of ##CF_4## and ##CHF_3## are: Here is how we draw the dipole moments:
Rules to draw dipole moments:
- The arrow direction is from the less electronegative element to the the more electronegative element, which depicts the direction on which the electrons are being pulled.
- Since we consider that carbon and hydrogen have similar electronegativity, there is no dipole moment between them or you could draw a very small arrow from hydrogen to carbon.
##CF_4## is a non-polar molecule because all dipole moments cancel out since it has a tetrahedral geometry, however, ##CHF_3## is a polar molecule since the dipole moments do not cancel out.
