Chalcogens are the family of elements on the Periodic Table known as Group 16 or the Oxygen Group. The name “chalcogen” comes from Greek words meaning “ore former” or “ore producer,” which is fitting since many metal ores exist as their compounds, particularly oxides and sulfides. These elements share distinct chemical behaviors due to their electron arrangement.
The Elements of Group 16
The chalcogen family consists of six elements: oxygen (O), sulfur (S), selenium (Se), tellurium (Te), polonium (Po), and the synthetic element livermorium (Lv). Oxygen and sulfur are the most well-known and abundant members; oxygen is the most abundant element in the Earth’s crust and the second most electronegative element.
The elements lower down the group, selenium and tellurium, are much rarer and are typically recovered as by-products of copper refining. Polonium is intensely radioactive and found only in trace amounts in uranium ores. Livermorium is a man-made element with a very short half-life, and its chemical properties are largely predicted.
Defining Chemical Characteristics
The unifying principle for all chalcogens is their electron configuration, as each atom possesses six electrons in its outermost energy shell (\(ns^2np^4\)). This structure dictates their chemical reactivity because they are two electrons short of achieving a stable, full-shell arrangement.
The most common way for chalcogens to achieve stability is by gaining two electrons, resulting in an oxidation state of -2. This tendency is strongest in oxygen, which is highly electronegative and forms ionic compounds like metal oxides. Heavier elements, such as sulfur, selenium, and tellurium, can also share their valence electrons to form covalent compounds with other nonmetals.
Unlike oxygen, the heavier chalcogens have accessible \(d\)-orbitals, allowing them to exhibit positive oxidation states such as +4 and +6. These higher oxidation states occur when the chalcogen bonds with a more electronegative element, such as fluorine or oxygen. This ability to adopt multiple oxidation states highlights a versatility in chemical bonding not seen in oxygen.
Physical Properties and Variability
The physical characteristics of the chalcogens change significantly moving down the group, a trend known as increasing metallic character. Oxygen is a nonmetal and exists as a colorless gas at room temperature, while sulfur is a nonmetal that exists as a soft yellow solid.
Further down, selenium and tellurium display properties between those of metals and nonmetals, classifying them as metalloids. Polonium is generally considered a metal, although it is highly radioactive. This transition from nonmetal gas to solid metalloid and then to radioactive metal illustrates the diverse nature of the group.
A common physical trait is the ability to form allotropes, which are different structural forms of the same element. Oxygen has two common allotropes: the diatomic molecule (\(\text{O}_2\)) necessary for respiration, and ozone (\(\text{O}_3\)) which forms a protective atmospheric layer. Sulfur is known to have over 20 allotropes, including the most stable eight-atom ring (\(\text{S}_8\)).
Common Uses and Importance
Chalcogens and their compounds are integral to both natural processes and industrial applications. Oxygen is fundamental to nearly all life on Earth, supporting aerobic respiration and fueling combustion. Its compounds, such as water, are the foundation of all known biology.
Sulfur is widely used in industry, primarily for the production of sulfuric acid, one of the most highly produced industrial chemicals globally. This acid is used in manufacturing fertilizers, detergents, and pigments. Sulfur is also used to vulcanize rubber, which improves the material’s elasticity and durability.
Selenium has specialized applications in electronics due to its photoconductivity, meaning its electrical conductivity increases when exposed to light. This property is utilized in photocopiers and laser printers. Biologically, selenium is a required trace element for human health, though it can be toxic at higher concentrations. Tellurium is often used in specialized alloys to improve material machinability and is also used in solar cells.