d- and f-Block Elements 

d-Block Elements (Transition Elements)

d-Block elements are those in which the differentiating electron enters the (n−1)d subshell. General electronic configuration: (n−1)d^1–10 ns^1–2.

Definition of Transition Elements

Elements having incompletely filled d-orbitals in the atomic state or in one of their common oxidation states.

Transition Series

• 3d-series: Sc (21) → Zn (30)
• 4d-series: Y (39) → Cd (48)
• 5d-series: La (57), Hf (72) → Hg (80)
• 6d-series: Ac (89) → Z = 112 (incomplete)

Important Notes

• Zn, Cd and Hg are not typical transition elements (d¹⁰ configuration).
• Cu, Ag and Au are considered transition elements due to variable oxidation states.
• All transition elements are d-block elements, but all d-block elements are not transition elements.

General Characteristics of Transition Elements

Physical Properties

• Hard, strong metals with high tensile strength
• Good conductors of heat and electricity
• High melting and boiling points
• Form alloys easily

Atomic and Ionic Radii

• Atomic radii decrease across a period but variation is small after the middle
• Radii of 4d and 5d elements are similar due to lanthanoid contraction
• Ionic radii decrease with increasing oxidation state

Density

• Density generally increases from left to right
• Os and Ir have very high densities

Melting and Boiling Points

• High due to strong metallic bonding
• W has the highest melting point
• Zn, Cd and Hg have low melting points

Ionisation Enthalpy

• Values lie between s- and p-block elements
• Increase across the period (not regular)
• Higher stability for half-filled and fully filled configurations (Cr, Cu)

Variable Oxidation States

• Due to participation of both ns and (n−1)d electrons
• Maximum variation shown by d⁵ configuration
• Highest oxidation state is +8 (OsO₄)
• Lower oxidation states are ionic; higher ones are covalent

Colour of Transition Metal Compounds

• Due to d–d transitions
• Colourless ions: Sc³⁺, Ti⁴⁺, Zn²⁺, Cu⁺
• Charge-transfer colours: Cr₂O₇²⁻, MnO₄⁻

Magnetic Properties

• Paramagnetism due to unpaired electrons
• Diamagnetic species have no unpaired electrons
• Magnetic moment: μ = √n(n + 2) B.M.

Complex Formation

• Due to small size, high charge and vacant d-orbitals

Catalytic Properties

• Due to variable oxidation states and surface adsorption

Inner-Transition Elements

Lanthanoids (4f-Block)

• Ce (58) → Lu (71)
• General oxidation state: +3
• Lanthanoid contraction due to poor shielding of 4f electrons
• Colours due to f–f transitions
• Most ions are paramagnetic

Actinoids (5f-Block)

• Th (90) → Lr (103)
• General electronic configuration: [Rn] 5f^1–14 6d^0–1 7s²
• Show greater range of oxidation states
• All actinoids are radioactive
• Actinoid contraction observed

Important Compounds (JEE Focus)

Copper Sulphate (CuSO₄·5H₂O)

• Blue vitriol; turns white on heating (anhydrous CuSO₄)
• Forms deep blue complex with NH₃ (Schweizer’s reagent)
• Used in electroplating and Bordeaux mixture

Potassium Dichromate (K₂Cr₂O₇)

• Strong oxidising agent
• Chromate–dichromate equilibrium depends on pH
• Used in tanning, glass cleaning and redox reactions

Potassium Permanganate (KMnO₄)

• Strong oxidising agent in acidic, neutral and alkaline media
• Purple crystals; tetrahedral MnO₄⁻ ion
• Used as disinfectant and in redox titrations

Important Metals

Iron (Fe)

• Oxidation states: +2, +3
• Cast iron, wrought iron and steel
• Steel carbon content: 0.25–2%

Copper (Cu)

• Oxidation states: +1, +2
• Refined by electrolytic refining

Silver (Ag)

• Oxidation state: +1
• Extracted by cyanide process

Mercury (Hg)

• Only liquid metal at room temperature
• Forms amalgams

Zinc (Zn)

• Oxidation state: +2
• Extracted from ZnS by roasting and reduction
• Used in galvanisation