Chemistry of Transition Elements

Topic Overview

• Chris Harris from Alle Chemistry introduced Topic 28 of CIE specifications focused on transition elements.
• Importance of understanding orbitals and electron movements from Year 1 Chemistry is emphasized.
• D block elements location and importance in the periodic table.

D Block Elements

• Located in the middle of the periodic table.
• Essential elements: Scandium, Titanium, Vanadium, Chromium, Manganese, Iron, Cobalt, Nickel, Copper, and Zinc.
• Transition elements: d block elements forming at least one stable ion with a partially filled d sub shell.

Period 4 d Block Elements

• Scandium and Zinc are not transition elements because they do not form stable ions with partially filled d sub shells.
• Electron configuration examples:
  • Titanium (Ti): 4s² 3d²
  • Vanadium (V): 4s² 3d³
  • Chromium (Cr): 4s¹ 3d⁵ (stability due to half-filled d sub shell)
  • Copper (Cu): 4s¹ 3d¹⁰ (stability due to fully filled d sub shell)
• Removal of electrons: 4s electrons are removed before 3d electrons.

Properties of Transition Metals

• Variable Oxidation States: Multiple oxidation states possible.
• Colored Ion Solutions: Transition metals form colored compounds based on their oxidation states and ligands.
• Catalytic Properties: Serve as good catalysts due to their variable oxidation states.
• Complex Formation: Can form complex ions by coordinating with ligands.

Colored Complexes and Oxidations States

Examples of Colors in Solution:

• Vanadium (V): V²⁺ is violet, V³⁺ is green, VO²⁺ is blue, VO2⁺ is yellow.
• Chromium (Cr): Cr³⁺ is violet (with water) and green (with other ligands), Cr₂O₇²⁻ is orange.
• Manganese (Mn): Mn²⁺ is pale pink, MnO₄²⁻ is green, MnO₄⁻ is purple.
• Iron (Fe): Fe²⁺ is green, Fe³⁺ is yellow.
• Cobalt (Co): Co²⁺ is pink.
• Nickel (Ni): Ni²⁺ is green.
• Copper (Cu): Cu²⁺ is blue.
• Titanium (Ti): Ti³⁺ is purple, Ti⁴⁺ is colorless.

Redox Titrations

• Used to determine the concentration of reducing or oxidizing agents.
• Example with Fe²⁺ and MnO₄⁻:
  • Fe²⁺ + MnO₄⁻ + H⁺ → Fe³⁺ + Mn²⁺ + H₂O
• Practical titration setup, endpoint detection, and calculations.
• Percentage compositions in tablets and other quantitative analyses.

D Orbitals

• Five d orbitals: d_xy, d_yz, d_zx, d_x² - y², and d_z²
• These orbitals can hold a total of 10 electrons.
• D orbital's shapes and orientations.

Complex Ions

• Complex ions consist of a central metal ion and surrounding ligands.
• Types of ligands: monodentate, bidentate, and polydentate.
• Coordination number depends on number of coordinate bonds.
• Shapes: Octahedral, tetrahedral, and square planar.

Stability Constants (K_stab)

• Stability of complexes is indicated by K_stab values.
• Higher K_stab implies more stable complexes.

Ligand Substitution and Stability

• Similar size ligands: Exchange without changing geometry.
  • Example: [Co(H₂O)₆]²⁺ + NH₃ → [Co(NH₃)₆]²⁺ + H₂O
• Different size ligands: Change in both shape and coordination number.
  • Example: [Cu(H₂O)₆]²⁺ + Cl⁻ → [CuCl₄]²⁻ + H₂O

Isomerism in Complexes

• Complexes can show optical isomerism (mirror-image isomers) and cis-trans isomerism.
• Cisplatin: An anti-cancer drug exhibiting cis-trans isomerism.

D Orbital Splitting

• The d orbital splits into two sets of orbitals in a complex due to ligand interaction, creating an energy gap (ΔE).
• Absorption of light causes electronic transitions between split d orbitals contributing to the color observed in complexes.

Summary

• Transition metals showcase unique properties such as variable oxidation states, colored ions, and complex formation which are central to their chemistry.
• Understanding electron configurations, complex ion formation, and ligand interactions are critical for mastering this topic.

Next Steps

• Engage with practice problems and visual aids (like periodic tables and orbital diagrams).
• Utilize provided videos and revision notes for a thorough understanding.

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