How can a molecule with polar covalent bonds be nonpolar?

Answer 1

It is possible for molecules with polar covalent bonds to be non-polar over all due to the geometry of the molecule.

For example,
Carbon Dioxide, CO2, has two polar,bonds between the Oxygen atoms and the Carbon atom...however, due to the linear geometry of the molecule, CO2 is non-polar.
O<--C-->O
The polar bonds point toward the Oxygen, but since they are Oxygen atoms on both sides, pulling on the electrons by equal amounts, the overall dipole moment is zero...they cancel each other out.

Carbon Dioxide is a rather simple example of the molecule's geometry causing an otherwise polar bonded molecules to be non-polar. There are more complex non-polar molecules, such as Carbon Tetrachloride, CCl4.
CCl4 has a tetrahedral shape which is near impossible for me to represent in ASCII are, but it looks like this,
http://upload.wikimedia.org/wikipedia/commons/d/df/Carbon_Tetrachloride.PNG
The C-Cl bonds are polar, but due to the geometry, it all cancels out to be non-polar.

Answer 2

If there is no dipole moment the the molecule cannot be polar.

like CCl4 is nonpolar because of the 4 chlorines....but im not sure if those bonds are polar covalent. Anyway good luck!

Answer 3

you have to give examlpe about what you want to tell

take care