Nonmetals typically have a negative charge when they form ions. This is because they tend to gain electrons to achieve a full valence shell, similar to the noble gases.
In their elemental state, nonmetals have a variety of oxidation states. However, when they form anions (negatively charged ions), they usually gain enough electrons to fill their outer shell. For example, chlorine (Cl), which is a nonmetal, gains one electron to become Cl– and achieves a stable electron configuration.
This tendency to gain electrons and form negative ions is a key characteristic of nonmetals, differentiating them from metals, which generally lose electrons to form positive ions.