Although non-metals can be gases, liquids or solids at room temperature, most are gases. These include hydrogen, helium, neon, nitrogen, oxygen, fluorine, argon, chlorine, krypton and xenon.
Non-metals have several physical and chemical properties that help distinguish them from metals. They do not conduct heat or electricity well. If a non-metal is a solid, it is brittle. Non-metals do not have a metallic gloss or "luster." When stretched into a thin sheet, a non-metal is transparent. Typically, non-metals have more electrons in their outer shells than metals do. Non-metals have four to eight, while metals contain only one to three. When a non-metal mixes with oxygen to form an oxide, it is an acidic substance.