The O-H, N-H, and F-H bonds are considered highly polar due to the significant electronegativity differences between the hydrogen atom and the atoms of oxygen, nitrogen, and fluorine.
Electronegativity is a measure of an atom’s ability to attract and hold onto electrons. Oxygen (O), nitrogen (N), and fluorine (F) are all located in the upper right section of the periodic table, which means they possess high electronegativities. Specifically, fluorine is the most electronegative element, followed by oxygen and then nitrogen.
In the case of the O-H bond, oxygen has an electronegativity of about 3.5, while hydrogen is only about 2.1. This difference leads to oxygen pulling the shared pair of electrons much closer to itself, creating a region of partial negative charge near the oxygen and a partial positive charge near the hydrogen.
Similarly, with the N-H bond, nitrogen has an electronegativity of approximately 3.0, again causing nitrogen to attract electrons more strongly than hydrogen, resulting in a polar bond.
For the F-H bond, the electronegativity of fluorine is around 4.0, which is even greater than that of oxygen or nitrogen. This leads to a very strong polar character as fluorine exerts a much stronger pull on the shared electrons than hydrogen.
Overall, the strong differences in electronegativity between hydrogen and these elements—oxygen, nitrogen, and fluorine—create bonds that have significant dipole moments, making them polar. This polarity is crucial in many chemical interactions, especially in biological systems, where hydrogen bonding plays a fundamental role in the structure and function of molecules.