Hydrogen bonding is a special case of very strong dipole-dipole interactions possible among only certain atoms. What atoms in addition to hydrogen are necessary for hydrogen bonding? How does the small size of the hydrogen atom contribute to the unusual strength of the dipole-dipole forces involved in hydrogen bonding?

Hydrogen bonding is a special type of dipole-dipole interaction that occurs between a hydrogen atom bonded to an electronegative atom (such as nitrogen, oxygen, or fluorine) and a lone pair of electrons on another electronegative atom. Therefore, in addition to hydrogen, the atoms necessary for hydrogen bonding are nitrogen, oxygen, and fluorine.

The small size of the hydrogen atom is crucial to the strength of hydrogen bonding. As the hydrogen atom has only one electron and occupies a minimal amount of space, the positively-charged nucleus is closer to, and thus more attracted to, the electronegative atom it is bound to. When a hydrogen atom is bonded to an electronegative atom, it experiences a significant difference in electronegativity, leading to the formation of a highly polar bond. Due to this high polarity and the close proximity of the hydrogen atom to the electronegative atom, a strong electrostatic attraction forms between the positive and the negative ends of these polar bonds. This results in a particularly strong dipole-dipole interaction called hydrogen bonding. In conclusion, the atoms necessary for hydrogen bonding are nitrogen, oxygen, and fluorine, in addition to hydrogen. The small size of the hydrogen atom allows it to be in close proximity to the electronegative atom it is bound to. This leads to a strong electrostatic attraction between the polar bonds, causing the increased strength of hydrogen bonding compared to other dipole-dipole interactions.