Final answer:
The directionality of hydrogen bonding is explained by dipole-dipole interactions, where the positive end of one dipole aligns with the negative end of another, creating an attractive force.
Step-by-step explanation:
We rationalize the directionality of hydrogen bonding through an understanding of dipole-dipole interactions. Hydrogen bonds are a subset of dipole-dipole interactions that occur specifically when hydrogen is covalently bonded to a highly electronegative atom like fluorine, oxygen, or nitrogen. In such cases, the hydrogen atom acquires a partial positive charge, and the electronegative atom it is bonded to has a partial negative charge. This polarity leads to an attractive force between the hydrogen of one molecule and the electronegative atom of a neighboring molecule. These interactions are directional because dipoles have positive and negative ends, creating a specific orientation in which molecules align themselves so that the positive end of one dipole is close to the negative end of another, leading to attraction.