Group 16 (Chalcogens): Oxygen, Sulfur, Selenium, Tellurium, Polonium, Livermorium

General characteristics

Chalcogens have the electronic configuration that ends in ns2 np4, which typically leads to common oxidation states of −2, +2, +4 and +6 depending on element and chemical context. Electronegativity and ionization energy decrease down the group while atomic radius and metallic character increase. Lighter members form stable oxides and oxyacids; heavier members form a variety of sulfides, selenides and tellurides. Many occur in minerals as sulfides (for example, iron sulfide) and as free sulfur in volcanic regions.

Elements and typical uses

• Oxygen: a diatomic gas essential for respiration and combustion; ozone (O₃) is an allotrope of atmospheric importance.
• Sulfur: a yellow solid with several allotropes (S₈ rings common); used to make sulfuric acid, fertilizers, vulcanized rubber and pesticides. More on sulfur.
• Selenium: a semiconductor and glass additive, important in electronics and as a trace nutrient; forms selenides and oxyacids. Selenium information.
• Tellurium: a rare, brittle metalloid used in alloys and thermoelectric materials; forms tellurides with many metals. Tellurium details.
• Polonium: a highly radioactive metal discovered in the late 19th century and used in specialized research and neutron sources; handled under strict controls. Polonium notes.
• Livermorium: a laboratory-produced, short-lived transactinide with no practical uses beyond nuclear research. Livermorium.

History and naming

The name "chalcogen" derives from Greek roots meaning "ore-former" because many metal ores are sulfides or other chalcogen compounds. Sulfur has been known since antiquity; oxygen was identified in the 18th century during studies of combustion and respiration. Selenium and tellurium were recognized in the 18th–19th centuries; polonium was discovered by the Curies in the 1890s; livermorium was synthesized in the laboratory in the early 21st century.

Biological and environmental roles

Oxygen sustains aerobic life; sulfur is a component of amino acids (cysteine, methionine) and vitamins; selenium is an essential trace element for certain enzymes but is toxic at higher concentrations. Chalcogen compounds also influence atmospheric chemistry (sulfur and nitrogen oxides affect acid rain; ozone affects UV shielding).

Notable distinctions

Across Group 16 there is a clear shift from nonmetal behavior (reactive gases and molecular solids) to metalloid and then metallic, radioactive behavior. Their chemistry is rich: sulfuric acid is a major industrial chemical, oxygen chemistry underpins respiration and combustion, and heavier chalcogens form important semiconducting and thermoelectric materials. Laboratory-only elements like livermorium illustrate limits of current synthesis and stability in the periodic table.