Sulfur and its compounds
Follow one element from yellow S8 crystals to sulfides, oxides, sulfuric acid and sulfates.
1. Sulfur is a group 16 nonmetal with six valence electrons. It commonly has oxidation states −2, +4 and +6; elemental sulfur is 0. The stable molecular form at room conditions is a puckered S8 ring. Orthorhombic and monoclinic sulfur contain S8 molecules packed differently, while rapidly cooled molten sulfur can form chain-rich plastic sulfur. These are allotropes: different structures of the same element.
Sulfur is a group 16 nonmetal with six valence electrons. It commonly has oxidation states −2, +4 and +6; elemental sulfur is 0. The stable molecular form at room conditions is a puckered S8 ring. Orthorhombic and monoclinic sulfur contain S8 molecules packed differently, while rapidly cooled molten sulfur can form chain-rich plastic sulfur. These are allotropes: different structures of the same element.
−2
In H2S and metal sulfides sulfur is usually −2. Many insoluble sulfides can be recognized by precipitate formation.
+4
SO2 and sulfites contain sulfur at +4. SO2 can be oxidized further and often acts as a reducing agent.
+6
SO3, H2SO4 and sulfates contain sulfur at +6, its highest common oxidation state.
2. A reaction pathway
- Burning sulfur forms sulfur dioxide: S + O2 → SO2.
- Further catalytic oxidation gives sulfur trioxide: 2SO2 + O2 ⇌ 2SO3.