Metals make up approximately three-fourths of the elements. This group can conduct electricity. Electric wires such as those inside a stereo set or lamp cord are composed of copper. A rubber covering keeps the wires from becoming too hot as electricity travels through them. A poor choice for wires, the metal aluminum would melt if enough electicity went through it. When exposed to water or air, some metals change chemically. Iron rusts when combined with oxygen. Nonmetals usually have properties opposite to metals. At room temperature, most nonmetals are all solids or gases. However, bromine is a(n) liquid at room temperature.