What distinguishes a covalent bond from an ionic bond?

The distinction between a covalent bond and an ionic bond fundamentally lies in the nature of electron interactions between the involved atoms. In covalent bonding, atoms share pairs of electrons, which allows them to achieve greater stability through the fulfillment of their valence shell requirements. This sharing often occurs between nonmetal atoms, which have similar electronegativities, enabling them to form strong, stable molecules.

On the other hand, ionic bonds are characterized by the transfer of electrons from one atom (typically a metal) to another (usually a nonmetal). This transfer creates charged ions: one atom becomes positively charged (cation) and the other negatively charged (anion). The opposite charges then attract each other, resulting in the formation of an ionic compound.

The explanation of the other options highlights their inaccuracies: covalent bonds do not exclusively involve metals, nor are they always weaker than ionic bonds, as their strength can vary depending on the specific atoms involved and their electronic configurations. Additionally, covalent bonds can form in different states of matter, including liquids and solids, not just gases. Thus, focusing on the sharing of electrons versus the transfer of electrons provides the clearest distinction between covalent and ionic bonds, solidifying the correctness of the chosen answer.