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Objective_Regret4763 t1_iv3uz51 wrote

In addition to what the other guy said, I teach AP chemistry and right now what is being taught at the advanced high school level is that if there is a molecular bond between elements that are not the same, then it is polar due to the inherent difference in electronegativity. For instance H2 or a carbon carbon bond would be non polar examples.

Also, what was not stressed in the other comment is the shape of the molecule. Carbon dioxide is linear

O=C=O so while the oxygen-carbon bonds are each polar due to O high electronegativity, the shape of the molecule will cancel out because of opposing pull of electrons. Same goes with something that is tetrahedral with polar bonds. The symmetrical shape cancels out the dipoles. So a shape that is not symmetrical such as the bent shape of water or ammonia, will have polar bonds AND be a polar molecule.

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Hidden-Felon OP t1_iv6hs1i wrote

>if there is a molecular bond between elements that are not the same, then it is polar

But aren't there some bonds between different elements that are nonpolar? Like CH4 the bond between carbon and hydrogen is nonpolar.

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Objective_Regret4763 t1_iv6qpvy wrote

In general, like in a lab setting, we would regard CH4 as a non-polar molecule overall. However, what has been agreed upon by the powers that be is that technically each individual C-H bond is in fact polar because of the difference in electronegativity of carbon and hydrogen. And technically this is a correct statement, no matter how small of a difference it might be.

It must also be recognized that there is a sliding scale of polarity that ranges from slightly polar like the example given, to very polar such as in water. To be fair this is getting very technical and for all intents and purposes, no one really talks about pure hydrocarbons as being polar molecules.

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