This lesson explains the properties, trends, complex formation, color, and catalytic behavior of transition metals—elements found in the d-block of the periodic table.

1. Core Concepts (Short Notes)

10.1 What Are Transition Metals?

Transition metals are elements that have partially filled d-orbitals in their atoms or ions.

• Typically found in Groups 3–12.

• Examples: Fe, Cu, Zn, Mn, Cr, Co, Ni.

10.2 General Physical Properties

• High density.

• High melting and boiling points.

• Good conductors of heat and electricity.

• Strong, malleable, and ductile metals.

10.3 Chemical Properties

• Form variable oxidation states (e.g., Fe²⁺, Fe³⁺, MnO₄⁻).

• Form colored compounds.

• Exhibit catalytic activity.

• Form complex ions with ligands.

• Show magnetic properties depending on unpaired electrons.

10.4 Variable Oxidation States

Transition metals can lose different numbers of electrons. Examples:

• Iron: Fe²⁺ (green), Fe³⁺ (yellow/brown)

• Copper: Cu⁺, Cu²⁺ (blue)

• Manganese: Mn²⁺, Mn⁷⁺ (purple permanganate)

10.5 Color of Transition Metal Compounds

Colors arise due to d–d electron transitions in the presence of ligands.

• Cu²⁺ → blue

• Ni²⁺ → green

• Cr³⁺ → violet or green

• MnO₄⁻ → purple

10.6 Catalytic Behavior

Transition metals and their compounds act as catalysts in many industrial processes:

• Fe in the Haber process.

• Ni in hydrogenation of oils.

• MnO₂ in decomposition of H₂O₂.

10.7 Complex Ion Formation

Transition metals form complex ions with ligands.

• Ligands: Molecules/ions donating electron pairs (e.g., H₂O, NH₃, Cl⁻).

• Example complex ions:

  • [Cu(H₂O)₆]²⁺ → blue

  • [Cu(NH₃)₄(H₂O)₂]²⁺ → deep blue

10.8 Magnetic Properties

• Unpaired electrons → paramagnetic.

• No unpaired electrons → diamagnetic.

2. Key Examples & Reactions to Remember

Haber Process Catalyst

N₂ + 3H₂ ⇌ 2NH₃ (Fe catalyst)

Oxidation States of Manganese

• Mn²⁺ (pale pink)

• MnO₄⁻ (purple)

• MnO₂ (brown solid)

Copper Complexes

• Cu²⁺ + 4NH₃ → [Cu(NH₃)₄]²⁺ (deep blue)

Chromium Compounds

• Cr³⁺ (green/violet)

• Cr₂O₇²⁻ (orange)

3. Tips & Tricks for Exams

• If a compound is colored, it likely contains a transition metal.

• Remember: Zn, Cd, and Hg are not considered transition metals because they have full d-sublevels.

• Complex ions often change color when ligands change (e.g., water to ammonia).

• Oxidation states above +3 are often strong oxidizing agents.

• Many transition metals show characteristic flame or solution colors.

• Use electron configuration to check if the d-orbital is partially filled.

4. Important Points to Remember

• Transition metals have diverse oxidation states.

• They form colored compounds due to d-electron transitions.

• They are widely used as catalysts in both laboratory and industry.

• Complex ion formation is a defining feature of d-block chemistry.

Magnetic properties depend on number of unpaired electrons.