d and f Block Elements JEE Main: Complete Guide

The d and f block elements chapter is a significant source of marks in JEE Main Inorganic Chemistry, contributing two to three questions per session. Transition metals (d block) are characterized by their variable oxidation states, catalytic activity, color of compounds, and magnetic properties — all of which JEE Main tests extensively. The lanthanides and actinides (f block) are tested primarily through their general characteristics and the important concept of lanthanide contraction. This guide covers the entire chapter with the level of detail JEE Main requires.

General Characteristics of Transition Metals

Transition metals are d-block elements with partially filled d orbitals either in the elemental form or in their common ions. Their characteristic properties stem from this electronic configuration. Variable oxidation states arise because both 4s and 3d electrons can be involved in bonding, and the energy gap between successive oxidation states is small. JEE Main tests the common oxidation states of the most important transition metals — particularly Cr, Mn, Fe, Co, Ni, and Cu — and the colors of their common ions and compounds.

The colors of transition metal compounds arise from d-d electronic transitions: electrons are excited from one d orbital to another by absorbing visible light, and the complementary color is transmitted or reflected. The color depends on the metal, its oxidation state, and the ligands surrounding it. JEE Main tests the colors of specific common compounds: the green color of Fe²⁺ solutions, the blue color of Cu²⁺ solutions, the violet color of KMnO₄, and the orange color of K₂Cr₂O₇. For the coordination chemistry context, connect with our coordination chemistry guide.

Magnetic Properties and Catalytic Activity

Transition metals and their compounds show paramagnetic behavior due to unpaired d electrons. The magnetic moment is calculated from the number of unpaired electrons, and JEE Main tests the ability to predict whether a transition metal ion is paramagnetic or diamagnetic from its electron configuration. Mn²⁺ has the most unpaired electrons (five) among the first-row transition metals and is therefore the most paramagnetic.

Transition metals serve as important industrial catalysts because they can adopt multiple oxidation states (allowing them to shuttle electrons), adsorb reactants on their surfaces (heterogeneous catalysis), and form intermediate compounds that provide lower activation energy pathways. JEE Main tests the catalytic roles of specific transition metals: Fe in the Haber process, V₂O₅ in the Contact process, Ni in hydrogenation of oils, and Pt in the Ostwald process. Take a free mock test on d-block elements to test your recall of these industrial applications.

Important Compounds of Transition Metals

JEE Main tests the preparation, properties, and uses of several specific transition metal compounds. Potassium dichromate (K₂Cr₂O₇) and potassium permanganate (KMnO₄) are the two most important, appearing in both inorganic chemistry and organic chemistry contexts as oxidizing agents. The preparation of K₂Cr₂O₇ from chrome ore involves the fusion of chromite with KOH in air, acidification, and crystallization. The preparation of KMnO₄ from MnO₂ involves alkaline oxidation followed by electrolytic oxidation.

The reactions of KMnO₄ in acidic, basic, and neutral media are extensively tested in JEE Main: in acidic medium it is reduced to Mn²⁺, in basic medium to MnO₄²⁻, and in neutral medium to MnO₂. The reactions of K₂Cr₂O₇ as an oxidizing agent in acidic medium — oxidizing Fe²⁺ to Fe³⁺, I⁻ to I₂, SO₃²⁻ to SO₄²⁻ — are also standard JEE questions. These appear both in inorganic chemistry and as oxidizing agents in organic reactions.

The f-Block Elements: Lanthanides and Actinides

Lanthanides are the 14 elements following lanthanum in which the 4f orbitals are progressively filled. Their most characteristic feature is the lanthanide contraction — the steady decrease in atomic and ionic radius across the series due to the poor shielding of the 4f electrons. The lanthanide contraction has important consequences: it explains why the atomic radii of the third-row transition metals are nearly the same as those of the corresponding second-row transition metals (affecting their properties dramatically), and why hafnium is the most difficult element to separate from zirconium.

Actinides are the 14 elements following actinium in which the 5f orbitals are filled. They are all radioactive. The early actinides (Th, Pa, U) show variable oxidation states similar to transition metals; the heavier actinides are predominantly in the +3 state like the lanthanides. JEE Main tests the general comparison of actinides with lanthanides: actinides have greater tendency toward complex formation, show more variable oxidation states, and their compounds are generally more intensely colored.

Revision Strategy

Organize your revision around the characteristic properties of transition metals (variable oxidation states, color, magnetism, catalysis) and the important compounds (KMnO₄, K₂Cr₂O₇). For f-block, focus on lanthanide contraction and the actinide comparison. This chapter connects to our p-block elements guide and our coordination chemistry guide. Sign up free to access our inorganic chemistry question bank.