Explain why in spite of nearly the same electronegativity, oxygen forms hydrogen bonding while chlorine does not.

Explanation

Although O and Cl have about the same electronegativity, yet their atomic size (covalent radii) are much different : O = 66 pm and Cl = 99 pm. As a rsult, electron density per unit volume on oxygen atom is much higher than that on chlorine atom. Therefore, oxygen forms hydrogen bonds while chlorine does not even though both have approx. The same electronegativity.