Chapter 6, Section 1
Metals, Nonmetals, and Metalloids
Most periodic tables are laid out like the one in Figure 6.5. Some elements from Periods 6 and 7 are placed beneath the table. This arrangement makes the periodic table more compact. It also reflects an underlying structure of the periodic table, which you will study in Section 6.2. Each group in the table in Figure 6.5 has three labels. Scientists in the United States used the labels shown in red. Scientists in Europe used the labels shown in blue. There is some overlap between the systems, but in many cases two different groups have the same letter and number combination.
For scientists to communicate clearly, they need to agree on the standards they will use. The International Union of Pure and Applied Chemistry (IUPAC) is an organization that sets standards for chemistry. In 1985, IUPAC proposed a new system for labeling groups in the periodic table. They numbered the groups from left to right 1 through 18 (the black labels in Figure 6.5). The large periodic table in Figure 6.9 includes the IUPAC system and the system used in the United States. The latter system will be most useful when you study how compounds form in Chapters 7 and 8.
Dividing the elements into groups is not the only way to classify them based on their properties. The elements can be grouped into three broad classes based on their general properties. Three classes of elements are metals, nonmetals, and metalloids. Across a period, the properties of elements become less metallic and more nonmetallic.
Metals
The number of yellow squares in Figure 6.5 shows that most elements are metals—about 80 percent. Metals are good conductors of heat and electric current. A freshly cleaned or cut surface of a metal will have a high luster, or sheen. The sheen is caused by the metal’s ability to reflect light. All metals are solids at room temperature, except for mercury (Hg). Many metals are ductile, meaning that they can be drawn into wires. Most metals are malleable, meaning that they can be hammered into thin sheets without breaking. Figure 6.6 shows how the properties of metals can determine how metals are used.
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Nonmetals
In Figure 6.5, blue is used to identify the nonmetals. These elements are in the upper-right corner of the periodic table. There is a greater variation in physical properties among nonmetals than among metals. Most nonmetals are gases at room temperature, including the main components of air—nitrogen and oxygen. A few are solids, such as sulfur and phosphorus. One nonmetal, bromine, is a dark-red liquid.
The variation among nonmetals makes it difficult to describe one set of general properties that will apply to all nonmetals. However, nonmetals are not metals, as their name implies. So they tend to have properties that are opposite to those of metals. In general, nonmetals are poor conductors of heat and electric current. Carbon is an exception to this rule. Solid nonmetals tend to be brittle, meaning that they will shatter if hit with a hammer.
Metalloids
There is a heavy stair-step line in Figure 6.5 that separates the metals from the nonmetals. Most of the elements that border this line are shaded green. These elements are metalloids. A metalloid generally has properties that are similar to those of metals and nonmetals. Under some conditions, a metalloid may behave like a metal. Under other conditions, it may behave like a nonmetal. The behavior often can be controlled by changing the conditions. For example, pure silicon is a poor conductor of electric current, like most nonmetals. But if a small amount of boron is mixed with silicon, the mixture is a good conductor of electric current, like most metals. Silicon can be cut into wafers, like those being inspected in Figure 6.7, and used to make computer chips.
Figure 6.7 Pancake-sized circular slices of silicon, called wafers, are used to make computer chips. Because a tiny speck of dust can ruin a wafer, the people who handle the wafers must wear “bunny” suits. The suits prevent skin, hair, or lint from clothing from entering the room’s atmosphere.