[[Matter and Chemical Bonding]]
[[electronegativity]]

when 2 bonding atoms have an $\Delta$ EN greater than 0.5 and less than 1.7, it's a polar covalent bond 

polar covalents have an imbalance of electrons, causing partial positive charges and partial negative charges, the atom with the stronger EN pulls the electron more but not enough to completely take it, making the electron closer and giving it a partial negative charge