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Nonmetals and their properties
The elements in Figure 9-8 are nonmetals. Nonmetals have properties that make them very different from metals. In this section you will study the properties of some important nonmetals.
Physical properties of Nonmetals
Metals are easy to recognize. They have many similar properties. In contrast, nonmetals can be very different from one another. Sulfur is yellow solid. The carbon in charcoal is a black solid. Anoher form of the same element carbon is diamond. Oxygen and hydrogen are both colorless gases.
Nonmetals are solids, gases, and include one liquid, bromine(Br). Solid nonmetals are brittle. A brittle substance breaks easily like a pretzel.
Nonmetals are not shiny, malleable, and ductile like metals. They are not good conductors of heat and electricity. Generally, the properties of nonmetals are just the opposite of the properties of metals.
Chemical properties of Nonmetals
You already know that the chemical properties of elements depend upon the electrons in the outermost energy levels of the atoms. Metals have three or fewer electrons in the outermost energy levels. Nonmetals have four to eight electrons in their outermost energy levels. Metals have a tendency to give away the few electrons in their outermost energy levels. Nonmetals have have a tendency to attract electrons to their outermost energy levels. As a result of this attraction, the outermost energy levels become filled with eight electrons. This difference in the number of electrons causes the difference in properties between metals and nonmetals. The outstanding chemical property of nonmetals is that they react with metals.
Families of Nonmetals
The nonmetals include some of the most important elements we know. Look at two important families of nonmetals.
The Halogens What do table salt, fluoride tooth-paste, and household bleach have in common? They all contain elements that belong to Group V11A, a family of , nonmetals called the halogens. Halogens combine readily with metals and form compounds called salts. A salt is a compound in which a metal is combined with one or more nonmetals. Ordinary table salt, for example, is a formed when the halogen chlorine reacts with the metal sodium.
The halogens have different physical properties. They are gaseous (fluorine, chlorine), liquid (bromine), and solid (iodine, astatine). The halogens are the most active of the nonmetals. None of them are found in the free, or uncombined, state in nature. They are always found as part of a compound. Each halogen has seven electrons in its outermost energy levels.
The Noble Gases Most elements in the Periodic Table will combine chemically with other substances. The Group V11A elements, however, combine with other elements only under very special conditions. These elements are called inert, or inactive.
The elements of Group V111A are oll colorless gases. It is known that kings and other nobles did not mix with their subjects. Since the gases in Group V111A did not appear to react chemically with any elements, these gases were named the noble gases. Since 1962, however, research chemists have been able to prepare several compounds of krypton(Kr) and xenon(Xe). Such compounds are very difficult to produce, so reactions with noble gases are still exceptional.
The elements in Group V111A have eight electrons in their outermost shells. Elements with this many electrons do not usually react with other elements. Table 9-3 gives some properties and uses of the noble gases.
Iodine is a disinfectant. It is added to table salt in the form of sodium iodine. This "iodized salt" helps to keep your thyroid gland working properly.
People in many regions of the world do not get enough iodine from the foods they eat. This shortage of iodine can cause growths called goiters to develop in the neck. Iodized salt is used in these regions to help prevent goiters from forming.
Before the introduction of iodized salt, many people developed goiters. Even Cleopatra was thought to have had a goiter. Compare her picture shown in Figure 9-9B with that of the person in Figure 9-9A. Did Cleopatra have a goiter? What do you think?