Chapter 6: Transition Elements

Elements with partially filled d or f subshells in atomic or ionic state. d-block (Outer transition), f-block (Inner transition/Lanthanides & Actinides).

• Typical Transition Elements: Group IIIB to VIIIB. Show variable valency, colored compounds.
• Non-Typical: Group IIB (Zn, Cd, Hg) have full d-orbitals. Group IIIB (Sc, Y) often form trivalent ions with empty d-orbitals.

• Binding Energy & MP/BP: High due to involvement of both ns and (n-1)d electrons in metallic bonding. Increases up to Group VIB (max unpaired e-) then decreases.
• Paramagnetism: Due to unpaired electrons. Max at middle of series (Mn, Fe).
• Color: Due to d-d transitions. Electrons absorb visible light to jump between split d-orbitals.
• Interstitial Compounds: Small atoms (H, C, N) trapped in crystal lattice. Hard, non-stoichiometric.

Compounds containing a central metal atom surrounded by ligands.

• Ligands: Electron pair donors. Monodentate (Cl-, NH3), Bidentate (Oxalate), Polydentate (EDTA).
• Coordination Number: Number of donor atoms attached.
• Chelates: Ring structures formed by polydentate ligands. More stable.
• Nomenclature: Cation named first. Ligands named alphabetically. Metal oxidation state in Roman numerals. Anionic sphere metal ends in '-ate'.

• Commercial Forms:
  • Pig/Cast Iron: 2.5-4.5% Carbon. Hard, brittle.
  • Wrought Iron: <0.12-0.25% Carbon. Purest form. Malleable.
  • Steel: 0.25-2.5% Carbon. Mild (0.1-0.2%), Medium (0.2-0.7%), High (>0.7%).
• Manufacture:
  • Open Hearth Process: Regenerative heat. Burning impurities (C, S, P) using Haematite.
  • Bessemer Process: Air blast through molten pig iron. pear-shaped converter.

Electric chemical decay of metals.

• Mechanism: Electrochemical theory. Galvanic cell formation. Fe acts as anode (oxidized), impurity as cathode.
• Prevention:
  • Tin Plating (Cathodic Coating): Fe coated with Sn. If damaged, Fe rusts faster (Fe is anode vs Sn). used for food cans.
  • Galvanizing (Anodic Coating): Fe coated with Zn. Zn sacrifices itself (Zn is anode vs Fe). Used for roofs, pipes.

Chromates (CrO4²⁻) & Dichromates (Cr2O7²⁻)

• Interconversion: 2CrO4²⁻ + 2H⁺ ⇌ Cr2O7²⁻ + H2O. Acid shifts eq to Dichromate (Orange), Alkali to Chromate (Yellow).
• Oxidizing Action: K2Cr2O7 in acid oxidizes H2S to S, FeSO4 to Fe2(SO4)3, KI to I2. Used in Chromyl Chloride test.

Potassium Permanganate (KMnO4)

• Preparation: From Pyrolusite (MnO2). Fused with KOH+Air → K2MnO4 (Green). Then oxidized to KMnO4 (Purple) electrolytically or by Cl2/CO2.
• Properties: Dark purple crystals. Strong oxidizing agent. Oxidizes Oxalic acid, FeSO4.