Many people believe that covalent bonds are always non-polar.
That’s not true! In fact, a covalent bond is likely to be polar when the electrons in one of the atoms.
Involved in bond formation has more than one pair of available orbitals.
When this happens, an electron from a higher energy level orbital will jump down and fill up some lower energy levels on the other atom.
This can cause dipoles to form in both atoms, which means they have opposite charges on different ends. References: -O’Grady, J.C., & Madura, G.J. (2012). Bonding and Molecular Properties of Covalent Molecules in the Gas Phase (Nobel Prize Lecture) International Journal of Chemical Kinetics 36(12), 11-157 DOI.
Rahman, M.A., Ahmad, A.H.M., Islam, K., & Rahman, G. (2016). Covalent Bonding and Molecular Properties of Hydrocarbons in the Gas Phase Journal of Physical Chemistry B 120(12), 2899-2906 DOI.