Which type of substances generally form covalent bonds?

Covalent bonds are formed when two nonmetals share electrons to achieve a stable electron configuration, typically following the octet rule. Nonmetals tend to have higher electronegativities, meaning they have a strong tendency to attract and share electrons rather than transfer them, which is characteristic of ionic bonds.

When nonmetals bond, they can form a variety of molecules with diverse properties, depending on how many electrons they share. This sharing of electrons allows each atom to attain a full valence shell, thus achieving stability. The result is a compound that can vary in polarity and strength based on the specific elements involved and the nature of the electron sharing.

In contrast, metals generally form metallic bonds characterized by a 'sea of electrons' that are delocalized across a lattice of positively charged ions, which is different from covalent bonding. Ionic compounds consist of metal and nonmetal combinations where electrons are transferred from the metal to the nonmetal, forming charged ions. Alloys, being combinations of metals, also do not fall under the category of substances that form covalent bonds.