Which statement describes covalent bonding?

• A. Metal + metal
• B. Ionic transfer of electrons
• C. Metal + nonmetal; electrons are shared
• D. Nonmetal + nonmetal; share electrons

Answer: (D)

Covalent bonds form when atoms share electrons to fill their outer electron shells, instead of transferring electrons to form ions. This sharing is most common between nonmetals with similar electronegativities, leading to molecules held together by shared electron pairs. In this view, the statement that describes covalent bonding is that nonmetals pair up and share electrons to complete their valence shells, as seen in molecules like H2 or CO2, where the bond results from each atom contributing electrons to a common shared region.

Metal–metal bonding describes metallic bonding, where electrons are delocalized in a "sea" around metal ions. Ionic bonding involves transfer of electrons from a metal to a nonmetal, creating ions that attract each other. A metal–nonmetal bond with sharing would mix concepts, but the classic covalent bond is specifically nonmetal–nonmetal sharing electron pairs.