Overview
This lecture explains how carbon in methane forms four identical bonds using sp³ hybrid orbitals and describes their geometry and bonding characteristics.
Methane Bonding and the Need for Hybridization
- Carbon's electron configuration (2s²2p²) suggests two types of orbitals (s and p) for bonding.
- Contrary to this, all four C-H bonds in methane are identical and arranged tetrahedrally.
sp³ Hybrid Orbital Formation
- Linus Pauling showed that one s orbital and three p orbitals hybridize to form four equivalent sp³ orbitals.
- The term sp³ indicates the combination of one s and three p orbitals, not the number of electrons.
- sp³ hybrid orbitals have two lobes and are unsymmetrical around the nucleus, leading to directional, strong bonds.
Geometry and Bond Strength in Methane
- Each sp³ orbital overlaps with the 1s orbital of hydrogen to form four identical C-H bonds in methane.
- Each C-H bond in methane has a bond strength of 439 kJ/mol (105 kcal/mol) and a bond length of 109 pm.
- The H-C-H bond angle in methane is 109.5°, called the tetrahedral angle.
- Methane adopts a tetrahedral geometry due to the orientation of the four sp³ hybrid orbitals.
Why Hybridization Leads to Strong Directional Bonds
- The larger lobe of the sp³ orbital overlaps strongly with hydrogen's 1s orbital, increasing bond strength.
- The asymmetry is due to the wave function signs of p and s orbitals combining during hybridization.
Key Terms & Definitions
- Hybridization — Mixing atomic orbitals to form new, equivalent hybrid orbitals for bonding.
- sp³ Hybrid Orbital — An orbital formed from one s and three p orbitals, oriented tetrahedrally.
- Tetrahedral Angle — The bond angle (109.5°) between atoms bonded to a central atom in a tetrahedral arrangement.
Action Items / Next Steps
- Review Figures 1.11 and 1.12 from the textbook for visual references of sp³ hybrid orbitals and methane’s structure.
- Read Section 1.7 for sp³ hybrid orbitals in ethane.