What is a hydrogen bond primarily characterized by?

A hydrogen bond is primarily characterized by the attraction between a slightly positive hydrogen atom and a slightly negative atom, typically oxygen or nitrogen. In a hydrogen bond, the hydrogen atom is covalently bonded to a highly electronegative atom, which gives the hydrogen a partial positive charge. This partial positive charge allows the hydrogen atom to be attracted to another electronegative atom, resulting in a hydrogen bond. This type of interaction is crucial in many biological and chemical processes, such as the structure of water and the stability of DNA.

The other choices refer to different types of interactions or bonds. For instance, the attraction between metallic atoms pertains to metallic bonding, which involves the sharing of free electrons among a lattice of metal atoms. The options referring to transferring electrons and sharing electron pairs pertain to ionic and covalent bonds, respectively, both of which involve different mechanisms of bonding compared to hydrogen bonds. Thus, the defining characteristic of a hydrogen bond as an attraction involving a positively charged hydrogen and a negatively charged atom sets it apart from these other types of bonding.