Manganese: position, atomic structure and some properties
Manganese is in period 4, side subgroup of group VII (VII B) (Z = 25), configuration [Ar] 3d⁵ 4s²; its stable oxidation states are +2, +4, +7. The main ore is pyrolusite MnO₂. The metal is obtained by reducing oxides with silicon or aluminium: 3Mn₃O₄ + 8Al → 9Mn + 4Al₂O₃. Manganese is a silvery hard metal covered with a thin oxide film; on heating with water Mn + 2H₂O → Mn(OH)₂ + H₂↑, with dilute acids it releases hydrogen: Mn + 2HCl → MnCl₂ + H₂↑, and with concentrated H₂SO₄ SO₂ forms. The oxide character changes with oxidation state: MnO and Mn₂O₃ are basic, MnO₂ is amphoteric, Mn₂O₇ is acidic. Potassium permanganate KMnO₄ is dark purple-red crystals and a strong oxidising agent; Mn⁷⁺ is reduced differently depending on the medium: in acidic medium to Mn²⁺ (almost colourless), in neutral medium to MnO₂ (brown precipitate), in alkaline medium to MnO₄²⁻ (green). For example: 2KMnO₄ + 5K₂SO₃ + 3H₂SO₄ → 6K₂SO₄ + 2MnSO₄ + 3H₂O. On heating KMnO₄ decomposes and gives oxygen: 2KMnO₄ → K₂MnO₄ + MnO₂ + O₂↑. Manganese is added to steel and alloys; dilute KMnO₄ solution is used in medicine as a disinfectant and MnSO₄ as a micro-fertiliser.
Make a table: “Medium” (acidic, neutral, alkaline), “Product of KMnO₄”, “Colour”. KMnO₄ is a strong oxidiser: mixing it with combustible substances (sugar, glycerol, alcohol) causes a fire or explosion hazard. Experiments with KMnO₄ solution are done by the teacher; for medical use follow only a doctor's advice.