Which elements are most likely to form covalent bonds?

Covalent bonds are most likely to form between nonmetals, which are elements located toward the right side of the periodic table.1

These elements typically have high ionization energies, meaning their atoms are reluctant to lose electrons to form ions. Because neither atom in a bond between two nonmetals can easily lose its valence electrons, they instead share them in pairs to achieve a more stable, lower-energy state, often following the octet rule.1243

In contrast, elements at the lower left of the periodic table are metals with low ionization energies; they tend to lose electrons to form positive ions, leading to ionic bonds when they react with nonmetals. While the distinction between bond types can sometimes be a matter of convenience, covalent bonding is the prevailing interaction when no metals are present in a compound.241