What characteristic defines nonmetals?

Nonmetals are defined by their characteristic of being poor conductors of heat and electricity. This trait is due to their atomic structure, which does not allow for the free movement of electrons, a property that is essential for conducting electricity. Additionally, nonmetals typically possess high electronegativities and ionization energies, which further contribute to their inability to conduct electricity effectively.

Nonmetals, such as oxygen and nitrogen, are generally found on the right side of the periodic table, contrasting with metals that dominate the left side. Because they do not easily transfer heat or electric current, nonmetals play critical roles in various chemical reactions and are often found in gaseous forms or as brittle solids.

This distinctive lack of conductivity is what primarily distinguishes nonmetals from metals, which are known for their excellent conductivity and shiny appearance.