Question

How do you distinguish between polar and nonpolar covalent bonds?

Answer 1

All covalent bonds between different atoms are polar to some extent, it's just that the properties associated with polar bonds are generally observed in the most polar ones.

Explanation:

Polarity is caused by a difference in electronegativity between the two atoms that are bonded. In reality, unless the two atoms are identical (e.g. `H_2` or `O_2`) there will always be a certain amount of polarity there, but for the really extreme cases you need to consider very large differences in electronegativity, for example, bonds between oxygen and hydrogen, or between oxygen and carbon.

As polarity increases, the more electronegative atom pulls the electron charge density towards itself giving itself a partial negative charge (and the other atom a partial positive one).