This image represents a famous ancient Egyptian named Tutankhamen. Do you see his heavy eyeliner? Most likely the eyeliner was made of a mineral containing antimony. This metalloid was commonly used for makeup by Egyptians between four and five thousand years ago. Today we know that antimony is toxic, although Tutankhamen probably didn’t know that. Antimony is found in group 15 of the periodic table. Group 15 is one of four groups of the periodic table that contain metalloids.
Groups 13–16 of the periodic table (orange in the Figure below ) are the only groups that contain elements classified as metalloids. Unlike other groups of the periodic table, which contain elements in just one class, groups 13–16 contain elements in at least two different classes. In addition to metalloids, they also contain metals, nonmetals, or both. Groups 13–16 fall between the transition metals (in groups 3–12) and the nonmetals called halogens (in group 17).
What Are Metalloids?
Metalloids are the smallest class of elements, containing just six members: boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te). Metalloids have some properties of metals (elements that can conduct electricity) and some properties of nonmetals (elements that cannot conduct electricity). For example, most metalloids can conduct electricity, but not as well as metals. Metalloids also tend to be shiny like metals, but brittle like nonmetals. Chemically, metalloids may behave like metals or nonmetals, depending on their number of valence electrons. You can learn more about specific metalloids by clicking on the element symbols in the periodic table at this URL: http://www.chemicool.com/ .
Q: Why does the chemical behavior of an element depend on its number of valence electrons?
Group 13: Boron Group
Group 13 of the periodic table is also called the boron group because boron (B) is the first element at the top of the group (see Figure below ). Boron is also the only metalloid in this group. The other four elements in the group—aluminum (Al), gallium (Ga), indium (In), and thallium (Tl)—are all metals. Group 13 elements have three valence electrons and are fairly reactive. All of them are solids at room temperature.
Boron is a very hard, black metalloid with a high melting point. In the mineral called borax, it is used to wash clothes. In boric acid, it is used as an eyewash and insecticide.
Group 14: Carbon Group
Group 14 of the periodic table is headed by the nonmetal carbon (C), so this group is also called the carbon group. Carbon is followed by silicon (Si) and germanium (Ge), which are metalloids, and then by tin (Sn) and lead (Pb), which are metals. Group 14 elements group have four valence electrons, so they generally aren't very reactive. All of them are solids at room temperature.
Germanium is a brittle, shiny, silvery-white metalloid. Along with silicon, it is used to make the tiny electric circuits on computer chips. It is also used to make fiber optic cables—like the one pictured here—that carry telephone and other communication signals.
Group 15: Nitrogen Group
Group 15 of the periodic table is also called the nitrogen group. The first element in the group is the nonmetal nitrogen (N), followed by phosphorus (P), another nonmetal. Arsenic (As) and antimony (Sb) are the metalloids in this group, and bismuth (Bi) is a metal. All group 15 elements have five valence electrons, but they vary in their reactivity. Nitrogen, for example, is not very reactive at all, whereas phosphorus is very reactive and found naturally only in combination with other substances. All group 15 elements are solids, except for nitrogen, which is a gas.
The most common form of the metalloid arsenic is gray and shiny. Arsenic is extremely toxic, so it is used as rat poison. Surprisingly, we need it (in tiny amounts) for normal growth and a healthy nervous system.
Group 16: Oxygen Group
Group 16 of the periodic table is also called the oxygen group. The first three elements—oxygen (O), sulfur (S), and selenium (Se)—are nonmetals. They are followed by tellurium (Te), a metalloid, and polonium (Po), a metal. All group 16 elements have six valence electrons and are very reactive. Oxygen is a gas at room temperature, and the other elements in the group are solids.
Tellurium is a silvery white, brittle metalloid. It is toxic and may cause birth defects. Tellurium can conduct electricity when exposed to light, so it is used to make solar panels. It has several other uses as well. For example, it makes steel and copper easier to work with and lends color to ceramics.
Q: With six valence electrons, group 16 elements need to attract two electrons from another element to have a stable electron arrangement of eight valence electrons. Which group of elements in the periodic table do you think might form compounds with elements in group 16?
A: Group 2 elements, called the alkaline Earth metals, form compounds with elements in the oxygen group. That’s because group 2 elements have two valence electrons that they are “eager” to give up. An example of a group 2 and group 6 compound is calcium oxide (CaO).
- Groups 13–16 of the periodic table contain one or more metalloids, in addition to metals, nonmetals, or both.
- Group 13 is called the boron group, and boron is the only metalloid in this group. The other group 13 elements are metals.
- Group 14 is called the carbon group. This group contains two metalloids: silicon and germanium. Carbon is a nonmetal, and the remaining elements in this group are metals.
- Group 15 is called the nitrogen group. The metalloids in this group are arsenic and antimony. Group 15 also contains two nonmetals and one metal.
- Group 16 is called the oxygen group. Tellurium is the only metalloid in this group, which also contains three nonmetals and one metal.
- metalloid : Class of elements that have some properties of metals and some properties of nonmetals.
Watch the video at the following URL, and then answer the questions below.
- Why does boron act chemically like a metal?
- Why do arsenic, antimony, and tellurium tend to have chemical properties similar to nonmetals?
- Sometimes silicon and germanium behave like metals, and sometimes they behave like nonmetals. Explain why.
- Which elements in groups 13–16 are metalloids?
- Name two physical properties that boron shares with most metals.
- What property of the metalloid silicon makes it useful for computer chips?
- A recent investigation found relatively high levels of the metalloid arsenic in samples of apple juice. Why might this be a serious problem?
- Why is the metalloid tellurium used to make solar panels?