Final answer:
Elements having three or fewer electrons in the outer energy level are classified as nonmetals. Nonmetals are typically dull, poor conductors of electricity and heat, and brittle when solid.
Step-by-step explanation:
Elements having three or fewer electrons in the outer energy level are classified as nonmetals. Nonmetals are typically dull, poor conductors of electricity and heat, and brittle when solid. They exist in all three states of matter, with most nonmetals being gases.