chalcogens

Chalcogens are the chemical elements in group 16 of the periodic table, consisting of oxygen (O), sulfur (S), selenium (Se), tellurium (Te), polonium (Po), and livermorium (Lv). They all have six valence electrons (ns2np4) and thus share chemical similarities, though their properties span nonmetals, metalloids, and a metal. The name derives from Greek words meaning “ore-forming,” reflecting their tendency to form ore minerals.

Most chalcogens form compounds with oxidation states from -2 to +6. In many sulfur-, selenium-, and tellurium compounds, the -2 state is common in sulfides, selenides, and tellurides, whereas higher oxides such as SO3, SeO3, TeO3, and the corresponding acids illustrate +4 and +6 states. Oxygen is highly electronegative and forms numerous oxides and oxoacids; down the group, elements become progressively more metallic in character.

Physically, oxygen is a colorless gas at room temperature; sulfur is a yellow solid; selenium and tellurium are semiconductors (selenium is a brittle red solid, tellurium a silvery metalloid); polonium is a highly radioactive metal; livermorium is synthetic and extremely short-lived, with little known chemistry.

Occurrence and importance: oxygen is the most abundant element by mass in Earth's crust and makes up about 21% of the atmosphere; sulfur is widespread in minerals and fuels; selenium occurs only in trace amounts but is essential in trace amounts for many organisms; tellurium and polonium are rare, with polonium produced in nuclear reactions. Livermorium has been produced in very small quantities in accelerators.

Applications: oxides and chalcogen compounds are central to chemistry and industry; oxygen is essential for respiration; sulfur compounds are used in fertilizers and chemistry; selenium compounds have specialized electronics and nutrition roles; tellurium is used in alloys and thermoelectrics; polonium historically served as a heat source in space equipment but is extremely hazardous.