The d- and f-block elements
Class 12 · Updated 2026-10-03. Published for practice.
Electronic configuration
Transition elements: partial filling of d orbitals (Groups 3–12). Common ions lose ns electrons before or with (n−1)d depending on stability (Cr, Cu exceptions you already met in Class 11).
Lanthanoids (4f): La to Lu; steady decrease in size (lanthanoid contraction) affects properties of elements after them. Actinoids (5f): radioactive, less regular — syllabus depth is lighter than lanthanoids.
Key properties
Variable oxidation states, coloured ions (d–d transitions), paramagnetism when unpaired d electrons exist, catalytic behaviour (Fe, V2O5, Ni surfaces).
Metallic character, high melting points, alloy formation. Oxides and hydroxides often amphoteric for high oxidation states (e.g. chromates, aluminates pattern at intro level).
Compounds worth naming
KMnO4 (oxidising agent in acid — link to your titration practical), K2Cr2O7 (oxidising agent in acid, orange), K2CrO4 / chromate–dichromate equilibrium in pH.
Potassium permanganate and dichromate preparations are industrial; in exams you balance redox with them as given oxidants.