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Metallic Properties
Elements can be categorized as metals or nonmetals based on physical and chemical properties. For example, metals readily give up valence electrons, and metallic oxides, such as quicklime, form alkaline substances when mixed with water. Directly testing a substance for these chemical properties, however, would require sophisticated test equipment or advanced scientific knowledge. Physical properties, on the other hand, are easier to test and observe because they relate to basic physical characteristics such as appearance and conductivity. You may find that mixtures and compounds that include nonmetallic substances exhibit physical properties of metals, but an important distinction is that metals exhibit these properties even in their pure or "elemental" form.
Visual Inspection
The first way to determine whether a substance is metal or nonmetal is simply to look at it. Virtually all metals are solid at room temperature, with the notable exception of mercury. Many nonmetals are gases at room temperature, though some are solids or liquids. Another distinctive visual characteristic of metals is a soft shine or sheen known as metallic luster. Nonmetals, in general, do not exhibit this luster. This simple test is not definitive, however, because some elements -- such as silicon, geranium and other "metalloids" -- exhibit characteristics of both metals and nonmetals.
Energy in Motion
Some of the electrons in metallic atoms are able to move freely from one atom to another. These mobile electrons are efficient carriers of energy -- the uniform movement of electrons creates electricity, and the random vibrations of freely moving electrons transfer heat. Thus, most metals are good conductors of both heat and electricity, and most nonmetals are not. The best way to test for electrical conductivity involves a tool known as a digital multimeter. Set the multimeter to measure resistance and touch the two probes to the material. If the measured resistance is very close to zero, the material conducts electricity and is almost certainly a metal. You can test for heat conduction by warming up the material and touching it with your fingertip; a metal will warm up your fingertip more quickly than a nonmetal.
The Hammer Test
Most metals are either malleable or ductile, usually both. Most solid nonmetals are neither malleable nor ductile. A malleable material is able to bend instead of break or crumble, and a ductile material can be stretched into a wire. Some metals, such as thick steel, cannot be bent or stretched without special equipment, but you can still manipulate your material in various ways and with various tools in an attempt to assess its general degree of malleability and ductility. For example, if your material is long and thin you can try to bend it by hand, and if it is thin and flat you can hit it with a hammer and look for a smooth indentation.