How must the electronegativies of two atoms compare if a covalent bond between themis to be polar?

Answer 1

The electronegativities must be far enough apart to be polar. If one atom has a 2.1 and the other a 4 electronegativity, then the molecule is polar. However, a 2.1 and a 2.3 would be close enough for uniform electron density.

Answer 2

The electronegativities of the two atoms must be different, with one atom being more electronegative than the other. This leads to an unequal sharing of electrons in the covalent bond, creating a dipole moment and resulting in a polar covalent bond.