Elements of the oxygen subgroup
The main subgroup of group VI holds oxygen O, sulfur S, selenium Se, tellurium Te and radioactive polonium Po; each has 6 outer electrons (ns²np⁴). They accept 2 electrons and show the oxidation state –2; oxygen is almost always –2 (–1 in H₂O₂, +2 in OF₂). Atoms of S, Se and Te have vacant orbitals in the outer shell, so they also show +4 and +6 (SO₂, SO₃); oxygen has no such orbitals. Sulfur occurs in nature free and in compounds: pyrite FeS₂, zinc blende ZnS, galena PbS, gypsum CaSO₄·2H₂O, Glauber’s salt Na₂SO₄·10H₂O. It has several allotropic forms: rhombic and monoclinic S₈ and plastic Sₙ. It is a yellow crystal, insoluble in water and not wetted by it (so ore is enriched by flotation), soluble in CS₂, and melts at about 113 °C. With metals and hydrogen it is an oxidizing agent (Fe + S → FeS, H₂ + S → H₂S), with oxygen and fluorine a reducing agent (S + O₂ → SO₂, S + 3F₂ → SF₆). Sulfur powder is flammable and burns to poisonous SO₂, so it must never be burned at home.
“Sulfur family”: on squared paper draw shell diagrams of O, S, Se, Te (2,6; 2,8,6; 2,8,18,6; 2,8,18,18,6). Below write the oxidation states and formulas. No substance is used and sulfur is not burned.