174 | The History and Use of Our Earth’s Chemical Elements As elements progress from group 13 to group 17, they show a shift from metallic char-

174 | The History and Use of Our Earth’s Chemical Elements As elements progress from group 13 to group 17, they show a shift from metallic char-

acteristics to properties of the nonmetals, but the distinctions are not cut-and-dried. Some elements listed in groups 13, 14, 15, and 16 may have both metal-like qualities—metalloids or semiconductors—as well as a few nonmetal properties.

There are several general ways to categorize elements in groups 13 to 16. These are metals different in several ways from the transition elements. They range from metallics (other met- als) to metalloids (semiconductors) to nonmetals. The elements in these groups are arranged according to their properties, characteristics, and the position of their electrons in their atom’s outer shells. These, and other factors, determine how they are depicted in the periodic table.

The metallics are often called “other metals” and begin an arrangement on the periodic table in zigzag steps. (You may view this dark zigzag line that divides the metallics from met- alloids on a copy of the Periodic table.) For the “other metals” or metallics, this zigzag line runs run from aluminum to gallium to indium to tin to thallium to lead and then ends with bismuth. Elements left of the zigzag are also called “poor metals.”

Some of the metalloids are considered semiconductors. The term “metalloids” is used in this reference book because these elements do have characteristics of both metals and non- metals, and the term “semiconductor” refers only to particular elements somewhere between metals and nonmetals. Semiconductors also have properties of both metals and nonmetals. Therefore, they have the ability to act as conductors of electricity and thermal energy (heat), as well as the ability to act as insulators or nonconductors of electricity and heat, depending upon the kind and amount of impurities their crystals contain. Again, following the zigzag steps on the periodic table, the metalloids having properties of both metals and nonmetals are as follows: boron, silicon, germanium, arsenic, antimony, tellurium, and polonium.

This book uses the vertical structure for listing the elements in groups 13 through 18 between periods 2 and 5. Therefore, the elements included as metallics, metalloids, nonmetals, and so on are arranged in a different order (vertical) according to their atomic numbers rather than following the zigzag line on the periodic table.

As mentioned, metalloids will, under certain circumstances, conduct electricity. Therefore, they are often called semiconductors. Elements listed as semiconductors or metalloids are crys- talline in structure. As very small amounts of impurities are added to their crystal structure, their capability of conducting electricity or acting as insulators increases or decreases. These impurities affect the capacity of electrons to carry electric currents. The flow of electricity is restricted according to the degree and type of impurities. This is why the “semi” is included in their name.

In contrast, nonmetals in groups 16 (VIA), 17 (VIIA), and 18 (VIIIA) are characterized by being very inefficient at conducting both electricity and heat. In fact, most can be thought of as “insulators” because they are such poor conductors of electricity and heat. To confuse mat- ters even more, some references list “semiconductors” as a special group of metals.

The Boron Group (Metallics to Semimetals): Periods 2 to 6, Group 13 (IIIA)