Chapter 1: d-Block Elements (Transition Metals)

Transition metals (Groups 3–12) have the outer configuration (n−1)$d^{1-10}$ $ns^{0-2}$. The two most tested anomalies are Cr ([Ar]3$d^{5}$ 4$s^{1}$, half-filled d stability) and Cu ([Ar]3$d^{10}$ 4$s^{1}$, fully-filled d stability). Both result from the migration of one 4s electron into 3d to achieve greater exchange energy. The five defining properties are variable oxidation states, coloured ions (d–d transitions in partially-filled d-subshells), paramagnetism (unpaired d-electrons, μ = √(n(n+2)) BM), catalytic activity (variable OS and surface adsorption), and ability to form coordination compounds. $MnO_{4}^{-}$ in three media gives: $Mn^{2+}$ (acidic, colourless, gains 5$e^{-}$), $MnO_{2}$ (neutral, brown, gains 3$e^{-}$), $MnO_{4}^{2-}$ (basic, green, gains 1$e^{-}$). $Cr_{2}O_{7}^{2-}$ (orange, acidic) converts to $CrO_{4}^{2-}$ (yellow, basic) on adding base; $K_{2}Cr_{2}O_{7}$ in acid reduces to green $Cr^{3+}$.

Chapter 2: f-Block Elements

The lanthanoid series fills 4f orbitals (La to Lu) and predominantly shows +3 oxidation state. Lanthanoid contraction — the steady decrease in $Ln^{3+}$ ionic radius from $La^{3+}$ (116 pm) to $Lu^{3+}$ (85 pm) — results from poor 4f shielding of nuclear charge. The key consequence: Period 5 (4d) and Period 6 (5d) elements in the same group have nearly identical atomic radii — Zr and Hf in Group 4 being the most important example for NEET. Actinoids fill 5f orbitals, show more variable oxidation states (+3 to +6), are all radioactive, and have more complex chemistry than lanthanoids. The actinoid contraction is more pronounced than the lanthanoid contraction due to even poorer 5f shielding.

Chapter 3: Coordination Compounds — Fundamentals

Werner's theory (1893): primary valence = oxidation state (ionisable); secondary valence = coordination number (non-ionisable, directional). The coordination sphere is written in square brackets. Ligand denticity: monodentate ($H_{2}O$, $NH_{3}$, $Cl^{-}$), bidentate (en, $ox^{2-}$), hexadentate (ED$TA^{4-}$). Ambidentate ligands ($NO_{2}^{-}$ through N or O; S$CN^{-}$ through S or N) cause linkage isomerism. IUPAC naming: ligands alphabetically → metal (Roman numeral OS) → anionic complex ends in -ate.

Chapter 4: Isomerism in Coordination Compounds

Geometrical isomerism: cis/trans in square planar $MA_{2}B_{2}$ (e.g., [Pt($NH_{3}$){2}$Cl_{2}$]) and octahedral $MA_{4}B_{2}$. Optical isomerism: non-superimposable mirror images; seen in tris-chelate complexes like [Co(en){3}]^{3+} (Λ and $\Delta$ enantiomers). Linkage isomerism: ambidentate ligand changes donor atom — [Co($NH_{3}$){5}($NO_{2}$)]^{2+} (nitro) vs [Co($NH_{3}$){5}(ONO)]^{2+} (nitrito). Ionisation isomerism: ligand and counter-ion exchange positions — [Co($NH_{3}$){5}Br]$SO_{4}$ vs [Co($NH_{3}$){5}$SO_{4}$]Br.

Chapter 5: Bonding Theories — VBT and CFT

VBT: inner orbital complexes use (n−1)d orbitals → d^{2}$$sp^{3} hybridisation → octahedral, low spin, often diamagnetic. Outer orbital complexes use nd → sp^{3}$$d^{2} → high spin, paramagnetic. CFT: d-orbitals split into t_{2}g (lower) and eg (higher) in octahedral field with energy gap $\Delta o$. In tetrahedral field, order is inverted (e lower, t_{2} higher) with $\Delta t$ = 4/9 $\Delta o$. Spectrochemical series: $I^{-}$ < $Br^{-}$ < $Cl^{-}$ < $F^{-}$ < $OH^{-}$ < $H_{2}O$ < $NH_{3}$ < en < $NO_{2}^{-}$ < $CN^{-}$ < CO. If $\Delta o$ > P → low spin; if $\Delta o$ < P → high spin. Energy of absorbed light = $\Delta o$; observed colour = complementary colour.