Chalcogens
The group 16 elements — oxygen, sulfur, selenium, tellurium and polonium — collectively known as the ore-forming elements.
Formula / equation
ns² np⁴
Unit
Dimensionless
In depth
Needing two electrons to complete an octet, chalcogens form −2 ions with metals and two covalent bonds with non-metals. Character shifts from strongly non-metallic oxygen to metallic polonium, and the heavier members display expanded octets in oxidation states up to +6.
Examples in the real world
Oxygen in water and oxides, sulfur in sulfide ores and H₂SO₄, and selenium in photocopier drums.