Main classes of inorganic compounds
Oxides are compounds of two elements, one of which is oxygen. They are basic (Na₂O, CuO), acidic (CO₂, SO₃, P₂O₅), amphoteric (ZnO, Al₂O₃) or neutral, non-salt-forming oxides (CO, NO); in peroxides (H₂O₂, Na₂O₂) oxygen has oxidation state –1. Bases consist of a metal atom and one or more hydroxide groups (OH); soluble bases are alkalis (NaOH, KOH, Ca(OH)₂). An acid contains hydrogen atoms that can be replaced by a metal plus an acid residue: HCl is monobasic, H₂SO₄ dibasic, H₃PO₄ tribasic. A salt consists of a metal (or NH₄⁺) and an acid residue and may be normal (NaCl), acidic (NaHCO₃), basic ((CuOH)₂CO₃), double or mixed. Genetic series: metal → basic oxide → base → salt; nonmetal → acidic oxide → acid → salt.
“Class map”: draw four columns on the board (oxide, base, acid, salt); students place formula cards (SO₃, KOH, HNO₃, CaSO₄, MgO, H₂S ...) in the right column and give the reason. Cards only.