Final answer:
A hydrogen bond is an attractive force between a covalently bonded hydrogen atom and a lone pair of electrons on a neighboring electronegative atom, contributing to the unique properties of substances like water.
Step-by-step explanation:
A hydrogen bond is an intermolecular or intramolecular attractive force that occurs when a hydrogen atom covalently bonded to a highly electronegative atom like nitrogen (N), oxygen (O), or fluorine (F) is attracted to a lone pair of electrons on a neighboring electronegative atom, usually within a polar molecule. The underlying mechanism involves the partial positive charge of the hydrogen atom due to the difference in electronegativity between hydrogen and the atom it is bonded to, which then gets attracted to the lone pair of electrons on another electronegative atom. Although hydrogen bonds are stronger than other types of dipole-dipole interactions, they are significantly weaker than covalent bonds, with a typical hydrogen bond being only about 5% as strong as a covalent bond.
The unique properties of water, such as its high boiling point and the behavior of acids in aqueous solutions, can be attributed to the formation of hydrogen bonds. For example, when acids dissolve in water, hydrogen bonding stabilizes the molecular dipoles and facilitates the process of acid dissociation, leading to the formation of hydronium ion (H3O+) and the corresponding anion (A-).