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A nonmetal is a chemical element that generally does not conduct heat or electricity very well, is usually a solid or a gas at normal temperatures, and (for solids) is difficult to reshape by pounding or beating. Nonmetals include elements such as carbon, sulfur, oxygen, and nitrogen. They are normally defined in contrast to metals, which are bright, shiny, solid elements (with one exception) that are good electrical and heat conductors. They are ductile, which means that pieces can be drawn into wires, and they are malleable, which means that they can be beaten into thin sheets. In chemical reactions, nonmetals usually react to make negativelycharged ions (anions) while metals usually react to make positively-charged ions (cations). Only about 20 elements are considered nonmetals, while the rest of them are considered metals. With the exception of hydrogen, all of the nonmetals are found in the right-hand side of the periodic table. In fact, many periodic tables have a bold line in a sort of stair-step shape in the right-hand side of the table. This bold line is the "border-line" between the metals and the nonmetals. Elements that are adjacent to the line share metal and nonmetal properties and are called metalloids or semi-metals.

There are some exceptions to the general properties of nonmetals. For example, carbon can conduct electricity, although it has all other nonmetal properties. Bromine is a liquid at normal temperatures, and it is the only liquid non-metal. All of the elements that are gases at normal temperatures are nonmetals. All of the metals, on the other hand, are solids at normal temperatures except for mercury, which is a liquid. (The element gallium melts at 91–93°F [31–32°C], which is just above room temperature.)

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