Transition Metals for JEE Main 2026: Complete Guide

Transition metals (d-block elements) exhibit a fascinating combination of properties — variable oxidation states, coloured compounds, magnetic behaviour, catalytic activity — all arising from their partially filled d-orbitals. JEE Main tests this chapter through properties of specific elements, configurations, and compounds of industrial importance. This guide covers every concept tested systematically.

Electronic Configurations and Variable Oxidation States

Transition metals have general configuration [noble gas] (n−1)d¹⁻¹⁰ ns¹⁻². In forming ions, the ns electrons are lost first (not nd). For Cr: [Ar] 3d⁵ 4s¹; Cr²⁺ is [Ar] 3d⁴; Cr³⁺ is [Ar] 3d³. For Fe: [Ar] 3d⁶ 4s²; Fe²⁺ is [Ar] 3d⁶; Fe³⁺ is [Ar] 3d⁵. Variable oxidation states arise because 3d and 4s energies are close — multiple oxidation states have comparable stability. Mn shows the widest range: Mn²⁺ to Mn⁷⁺. The most stable oxidation state for most first-row transition metals is +2 (for Mn, especially stable as Mn²⁺ for half-filled 3d⁵ stability). For the coordination chemistry applications see our coordination chemistry guide.

Magnetic Properties

Paramagnetism arises from unpaired electrons; diamagnetism from all-paired electrons. Magnetic moment μ = √(n(n+2)) BM, where n = unpaired electrons. The highest magnetic moment first-row ion: Mn²⁺ or Fe³⁺ (both d⁵ high-spin, n = 5, μ = √35 ≈ 5.92 BM). Zn²⁺ (d¹⁰) and Ti⁴⁺ (d⁰) are diamagnetic. JEE regularly asks to identify ions from their magnetic moment or to rank paramagnetism — count unpaired electrons from the configuration.

Colour and Catalysis

Transition metal compounds are coloured because of d-d electron transitions in the visible spectrum. Sc³⁺ (d⁰), Zn²⁺ (d¹⁰), and Ti⁴⁺ (d⁰) are colourless because they cannot undergo d-d transitions. Transition metals and their compounds are excellent catalysts: Fe in Haber process (N₂ + 3H₂ → 2NH₃); V₂O₅ in Contact process (SO₂ → SO₃); MnO₂ in Cl₂ production; Ni in hydrogenation of oils. The catalytic action involves variable oxidation states providing reaction pathways of lower activation energy.

Important Compounds: Dichromate, Permanganate, and Ferrate

Potassium dichromate K₂Cr₂O₇: orange, strong oxidising agent in acidic medium. Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O (Cr goes from +6 to +3). Potassium permanganate KMnO₄: deep purple, powerful oxidising agent. In acid: MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O (colourless, Mn +7 to +2). In neutral/alkaline: MnO₄⁻ → MnO₂ (brown). KMnO₄ is used to distinguish alkenes (decolourise KMnO₄ solution) and in titrations. These reactions are memorised as standard half-equations for JEE redox problems.

Alloy Formation and Interstitial Compounds

Transition metals form alloys with other metals and interstitial compounds with small atoms (H, C, N, B) that occupy the holes in the crystal lattice. Interstitial compounds (e.g. TiC, steel = Fe+C) are hard, chemically inert, and have high melting points. They are non-stoichiometric (variable composition). Steel owes its hardness to interstitial carbon atoms distorting the iron lattice. JEE tests both the concept of alloy vs. compound and the specific properties of interstitial compounds. After reviewing all transition metal properties, take a free mock test on d-block elements.