VIDEO: CH. 19 Valence Bond Theory

Overview

This lecture reviews Valence Bond Theory (VBT) to explain bonding and geometry in complex ions, focusing on hybridization, shapes, and application to transition metal complexes.

Valence Bond Theory Basics

• VBT describes covalent bonding by mixing atomic orbitals to form hybrid orbitals.
• Carbon can form four single covalent bonds using sp³ hybridization, leading to tetrahedral geometry (bond angles of 109.5°).
• Hybrid orbitals (sp³, sp², sp) explain different bonding patterns and shapes in molecules.

Applying VBT to Complex Ions

• Complex ions consist of a central metal ion bonded to ligands through coordinate covalent (dative) bonds.
• The metal ion acts as a Lewis acid (electron acceptor), while the ligand acts as a Lewis base (electron donor).
• Overlap between filled ligand orbitals and empty metal orbitals forms sigma bonds in complex ions.

Hybridization and Geometry in Complex Ions

• Coordination number equals the number of ligands attached to the central metal ion.
• The type of hybrid orbitals formed depends on the coordination number and determines molecular geometry:
  • Linear: 2 ligands, sp hybridization, 180° bond angle.
  • Tetrahedral: 4 ligands, sp³ hybridization, 109.5° bond angle.
  • Square planar: 4 ligands, dsp² hybridization, 90° bond angles.
  • Octahedral: 6 ligands, d²sp³ hybridization, 90° bond angles.
• d orbitals participate in bonding for transition metals, so notations like dsp² (square planar) and d²sp³ (octahedral) are used.

Examples

• [Pt(NH₃)₄]²⁺: Square planar, 4 ligands, dsp² hybridization.
• [CoBr₂(H₂O)₄]: Octahedral, 6 ligands, d²sp³ hybridization.

Key Terms & Definitions

• Valence Bond Theory (VBT) — a model for describing covalent bonding via hybridization of atomic orbitals.
• Hybridization — mixing of atomic orbitals to form new hybrid orbitals for bonding.
• Coordination Number — the number of ligand atoms attached to a central metal ion.
• Ligand — molecule or ion that donates electron pairs to a central metal ion.
• Coordinate Covalent Bond — bond where both electrons come from the same atom (ligand).
• Lewis Acid/Base — acid is the electron pair acceptor (metal), base is the donor (ligand).

Action Items / Next Steps

• Create flashcards summarizing VBT for complex ions: hybridizations, geometries, bond angles, and key definitions.
• Review ligand charts and practice identifying coordination numbers for given complexes.
• Prepare for questions requiring assignment of hybridization and geometry based on complex formulas.