The group in the periodic table that contains only nonmetals is Group 18, also known as the Noble Gases. This group includes elements like Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn).
Noble gases are unique because they have complete valence electron shells, which makes them extremely stable and generally unreactive. Unlike metals and metalloids that exhibit a range of chemical behaviors, noble gases are found in nature primarily as isolated atoms. Their lack of reactivity and distinct properties are what categorize them distinctly as nonmetals.