Predicting Polarity: Molecule Dipole Moment Questions

[professor]

how do i tell when a molecue is poler... i know its when it was dipole moment that do not cancel each other... but how do i know when a molecule had dipole moments... this one is really stunmping me...nad about all thses questions... no I am not reading them off a list... this is a few moths of questiones on summer work i dident understand stored up

 

[whozum]

The molecule is polar if the center of charge does not coincide with the center of the molecule. Usually nonpolar molecules are symmetric in shape, for example CH4 and CF4 are non polar because all four hydrogens and flouride's charge cancel each other out. An example of a polar molecule for example is OH, since oxygen is much more electronegative than hydrogen, it pulls the electrons closer to it and the center of charge is shifted a bit more to the oxygen.

Drawing the molecular configuration helps a lot in these problems.

The very primitive 80% rule, if its symmetric, its nonpolar.

 

[professor]

thank you- great help

yes...i get it!