Partial positive and partial negative charges are [roduced when a shared pair of electrons in a covalent bond are attracted more by one atom on one side of the bond more than the atom on the other side, due to differences in their electronegativities. Thus partial charges develops on thse atoms. A partial positive charge develops on the atom which has less electronegativity and a partial negative charge develops on the atom which has high electronegativity.

Example, in a molecule of water, the shared pair of electrons between hydrogen and oxygen is pulled more towards oxygen. This is because oxygen is more electronegative and can attract the electrons more than hydrogen, which has very less electronegativity. Therefore, hydrogen develops a partial positive charge and oxygen gets a partial negative charge.