Question

What do polar covalent bonds result from?

Answer 1

The difference between electronegativity of the binding atoms.

Explanation:

(Refer to the periodical table element with electronegativity value)
Consider a bond to be non-polar if this difference is smaller than `0.4` (or `0.2 ~ 0.5` in certain cases )
Also, bonds are no longer considered "covalent" if the difference is greater than `2.0`, as electron "transfer" occurs.