Transition Elements and d Orbitals

d Orbitals and Transition Elements

• d orbitals of transition elements extend more towards the periphery of an atom than s and p orbitals, allowing them to significantly interact with their surroundings.
• Ions with a d configuration (n = 1 – 9) often display comparable magnetic and electronic properties.
• Partially filled d orbitals lead to unique characteristics, including multiple oxidation states, formation of colored ions, and the ability to create complexes with various ligands.
• Transition metals are recognized for their catalytic properties and paramagnetic behavior.
• Properties of transition metals show more similarities across a horizontal row compared to non-transition elements.

Transition Element Qualification

• Scandium (Z = 21) is classified as a transition element due to its ground state having an incompletely filled 3d orbital (3d¹).
• Zinc (Z = 30) is not a transition element since its 3d orbitals are completely filled in both the ground and oxidized states.

Ionization Energies and Trends

• Ionization energies rise slightly across the 3d series; higher-charged ions (d configurations without 4s electrons) reflect greater effective nuclear charge.
• A predictable increase in second ionization enthalpy may be interrupted at Mn²⁺ and Fe³⁺ due to their d⁵ configurations.
• Ionization enthalpy variations are influenced by electron-nucleus attraction, electron-electron repulsion, and exchange energy due to degeneracy in orbitals.

Exchange Energy and Stability

• Exchange energy correlates with the number of possible parallel spin pairs in degenerate orbitals, favoring configurations based on Hund’s rule.
• Increased stability from exchange energy loss makes ionization more challenging; no loss occurs at d⁶ configurations.
• For example, Mn⁺ has a 3d⁵4s¹ configuration, resulting in lower ionization enthalpy compared to Cr⁺ (d⁵).

Complex Compound Formation

• Transition metals readily form numerous complex compounds due to their small ionic sizes, high charges, and availability of d orbitals.
• Notable examples of complex compounds include [Fe(CN)₆]²⁺ and [Cu(NH₃)₄].

Catalytic Properties

• Transition metals and their compounds act as catalysts due to their ability to adopt various oxidation states and form complexes.
• Examples include vanadium(V) oxide in the contact process and finely divided iron in the Haber process.
• Catalysis involves bonds formation between reactants and catalyst surfaces, enhancing reactant concentration while lowering activation energy.

Interstitial Compounds

• Formed when small atoms (H, C, N) fit into metal crystal lattices.
• Reaction kinetics, alongside redox potential, is critical in understanding slow reactions, like H₂O oxidation by permanganate.

Oxidizing Reactions of KMnO₄

• KMnO₄ reacts with various substances under acidic conditions, yielding distinct products:
  • Iodine liberation from KI.
  • Conversion of Fe²⁺ (green) to Fe³⁺ (yellow).
  • Oxidation of oxalate ions to CO₂.
  • Oxidation of hydrogen sulfide to sulfur.
  • Oxidation of sulfite to sulfate.
  • Oxidation of nitrite to nitrate.

Characteristics of Lanthanoids

• Hardness increases with atomic number; samarium is notably hard.
• Melting points range from 1000 K to 1623 K for samarium.
• Lanthanoid ions exhibit color due to f-electron presence, except for La and Lu.
• First ionization enthalpy averages around 600 kJ mol⁻¹, with second ionization about 1200 kJ mol⁻¹.
• Chemical reactivity trends from calcium-like behavior in early members to aluminum-like traits in heavier members.