When a hydrogen atom covalently bonds to one oxygen or nitrogen atom, it is considered to have a partial positive charge. This is because the electronegativity of oxygen and nitrogen is greater than that of hydrogen, meaning that they attract electrons more strongly. As a result, the electrons in the covalent bond are pulled towards the oxygen or nitrogen atom, leaving the hydrogen atom with a slight positive charge.

This partial positive charge on the hydrogen atom can then attract another atom or molecule, such as a second oxygen or nitrogen atom, to form a hydrogen bond. Hydrogen bonds are weaker than covalent bonds, but they can still play an important role in determining the structure and properties of molecules and materials. For example, hydrogen bonds are responsible for the high boiling point of water and the solubility of many polar molecules in water.