What type of bond is formed when two non-metals react?

When two non-metals react, they typically form a covalent bond. This type of bond involves the sharing of electrons between the atoms of the non-metals. Since both non-metals have similar electronegativities, they generally do not transfer electrons to each other as metals would; instead, they achieve stability by sharing pairs of electrons.

In many cases, this means that both atoms attain a full valence shell, following the octet rule, which leads to the formation of a stable molecule. For instance, in the case of hydrogen chloride (HCl), hydrogen and chlorine share electrons, resulting in a covalent bond that holds the two atoms together.

The other types of bonds mentioned do not form between non-metals. An ionic bond typically occurs between a metal and a non-metal, where electrons are transferred rather than shared. Metallic bonds consist of a 'sea' of delocalized electrons and occur between metal atoms. A composite bond is not commonly recognized in chemistry as a standard bond type. Therefore, the correct answer is the covalent bond, highlighting the nature of bonding between non-metal elements.