The periodic table organizes chemical elements based on their shared characteristics, allowing scientists to predict their behavior. Elements are broadly categorized as metals, nonmetals, or metalloids. These classifications are based on a combination of physical and chemical properties, such as luster, malleability, and electrical conductivity. The periodic table’s structure, particularly the vertical columns (groups), illustrates this progression. Focusing on Group 16 reveals a clear transition in properties, moving from the top of the column to the bottom.
The Chalcogens: Elements of Group 16
Group 16, sometimes called the Oxygen Group, contains elements that illustrate a fundamental trend: increasing metallic character as atomic number increases. The group begins with Oxygen (O) and Sulfur (S), both definitive nonmetals that are poor conductors of electricity. Moving down the group, the elements begin to display a blend of properties, making the metalloid classification relevant. Tellurium (Te) and Polonium (Po) follow, along with the synthetic and highly radioactive Livermorium (Lv). Polonium, situated at the bottom of the naturally occurring elements, is a metal. This progression from nonmetal (Oxygen) to metal (Polonium) makes Group 16 an excellent example of how elemental properties change, requiring focus on the elements positioned between the clear nonmetals and the metal.
Defining the Properties of Metalloids
Metalloids possess characteristics intermediate between those of true metals and nonmetals. They are typically found in a diagonal “stair-step” region of the periodic table, separating the metals to the left from the nonmetals to the right. Physically, metalloids often have the shiny appearance of a metal but are brittle, meaning they shatter easily when struck, much like nonmetals.
The most distinctive feature of metalloids is their electrical conductivity, which is moderate compared to metals and nonmetals. They are commonly known as semiconductors, a property vital for modern technology. Unlike metals, the conductivity of a semiconductor can be precisely controlled. For example, conductivity can be increased by changes in temperature or by introducing small amounts of impurities, a process called doping. This ability to regulate the flow of electricity makes these elements indispensable in the manufacture of microchips and other electronic components. They also exhibit intermediate chemical behavior, such as forming covalent bonds, a characteristic usually associated with nonmetals.
Identifying the Group 16 Metalloid
Within Group 16, Tellurium (Te) is the element most consistently and universally classified as a metalloid. Tellurium displays the classic intermediate properties, appearing as a lustrous, silvery-white solid with a metallic sheen, yet it is brittle and easily pulverized. Its electrical characteristics confirm this designation, as crystalline tellurium exhibits the electronic band structure of a semiconductor.
Tellurium’s neighbor, Selenium (Se), sometimes causes confusion regarding the metalloid classification. Selenium exhibits photoconductivity, meaning its electrical conductivity increases significantly when exposed to light, which has led to its use in photocells. However, in its most common forms, Selenium’s chemical properties and overall behavior lean more toward that of a nonmetal. While Selenium is sometimes considered a borderline case, Tellurium reliably fits the full definition of a metalloid.
The semiconducting ability of Tellurium makes it valuable in technology, particularly in thin-film solar cells. Its compound cadmium telluride (CdTe) is used to efficiently convert sunlight into electricity. Tellurium represents the transitional nature of its position, possessing the physical look of a metal but the finely tunable electrical properties of a semiconductor. The element Polonium (Po), which follows Tellurium, completes the shift by behaving primarily as a metal. Tellurium is thus the definitive Group 16 element that bridges the gap between the nonmetallic and metallic elements.