Group 16: the oxygen group (chalcogens)

Six outer electrons: ns² np⁴

Each configuration ends in ns² np⁴, as in oxygen ([He] 2s² 2p⁴) and sulfur ([Ne] 3s² 3p⁴). Gaining two electrons gives ions with a 2− charge, such as the oxide ion O²⁻ and the sulfide ion S²⁻, while sharing two gives molecules such as water (H₂O) and hydrogen sulfide (H₂S).

Oxygen is almost always −2, but sulfur, selenium and tellurium can also reach +4 and +6, as in sulfur dioxide (SO₂) and sulfuric acid (H₂SO₄). Polonium, at the bottom, forms +2 and +4 compounds.

Trends down the group

Electronegativity falls from 3.44 for oxygen, second only to fluorine, to 2.58 for sulfur, 2.1 for tellurium and 2.0 for polonium. Oxygen is a gas that melts at 54.36 K, while sulfur melts at 388.36 K, selenium at 494 K and tellurium at 722.66 K. Density climbs from 2.07 g/cm³ for sulfur to 6.24 g/cm³ for tellurium and 9.196 g/cm³ for polonium.

The character of the elements changes with these numbers: oxygen, sulfur and selenium are nonmetals, tellurium is a metalloid, and polonium is a radioactive metal.

Where you meet group 16

You breathe oxygen, and it makes up most of the mass of water and nearly half the mass of Earth’s crust. Sulfur is turned into sulfuric acid and hardens rubber for tires, and sulfur compounds give rotten eggs and skunk spray their smell. Selenium is a trace nutrient found in Brazil nuts, and tellurium is used in thin-film solar panels and rewritable discs.

Ore makers and a dangerous metal

The name chalcogen means ore former, because many metal ores are oxides or sulfides. Polonium, discovered by Marie and Pierre Curie in 1898 and named after Poland, is intensely radioactive and extremely toxic. Livermorium (116), named after the Lawrence Livermore National Laboratory, has been made only a few atoms at a time, so its properties are predicted, not measured.