Here's why:

* Electronegativity: Nonmetals have higher electronegativity than metals. This means they have a stronger attraction for electrons.

* Electron Configuration: Nonmetals typically have nearly filled outer electron shells. Gaining one or more electrons completes their shell and makes them more stable.

When nonmetals bond with metals, the metal atoms lose electrons to become cations (positively charged ions), and the nonmetals gain those electrons to become anions (negatively charged ions). This results in an ionic bond.

Examples of common anions:

* Halogens: Fluorine (F-), Chlorine (Cl-), Bromine (Br-), Iodine (I-)

* Oxygen: Oxide (O2-)

* Sulfur: Sulfide (S2-)

* Nitrogen: Nitride (N3-)

Exceptions:

While nonmetals generally form anions, there are some exceptions. For example, hydrogen can form a cation (H+) in some compounds.