Overview
This lecture explains the concept of hybridization of atomic orbitals, types of hybrid orbitals, their characteristics, and how they relate to sigma and pi bonds.
Introduction to Hybridization
- Hybridization involves combining atomic orbitals to form new, hybrid orbitals.
- Examples: sp³ (1 s + 3 p), sp² (1 s + 2 p), sp (1 s + 1 p), d²sp³ (2 d + 1 s + 3 p).
- Hybrid orbitals are used in bond formation within molecules.
Atomic Orbitals
- s orbital is spherical and represents the probability region for an electron.
- p orbitals come in three types: px (x-axis), py (y-axis), pz (z-axis).
- Orbitals show where electrons are most likely found due to the uncertainty principle.
Hybridization of Carbon
- Carbon’s electron configuration: 1s² 2s² 2p²; it has 4 valence electrons.
- sp³ uses 1 s and 3 p orbitals, forming 4 degenerate (equal energy) hybrid orbitals.
- sp³ orbitals have 25% s character and 75% p character, closer in energy to 2p than 2s.
- Place one electron in each degenerate orbital before pairing, following Hund’s rule.
sp² and sp Hybrid Orbitals
- sp² formed from 1 s and 2 p orbitals, producing 3 degenerate orbitals, 33% s and 67% p.
- Remaining p orbital in sp² is unhybridized, available for pi bonding.
- sp formed from 1 s and 1 p orbital, creating 2 degenerate orbitals, both 50% s/50% p.
- Unused p orbitals in sp hybridization remain unhybridized.
Sigma (σ) and Pi (π) Bonds
- Hybrid orbitals mainly form sigma (σ) bonds; unhybridized p orbitals form pi (π) bonds.
- Every single bond has one sigma bond; double bonds have one sigma and one pi bond; triple bonds have one sigma and two pi bonds.
- Sigma bonds are stronger than pi bonds.
- Triple bonds are stronger and shorter than single bonds due to more total bonds.
Counting Sigma and Pi Bonds
- Each bond includes one sigma bond.
- Each double bond contains one pi bond; each triple bond has two pi bonds.
- To count: total number of bonds = sigma bonds; count double/triple bonds for pi bonds.
Key Terms & Definitions
- Hybridization — mixing atomic orbitals to create new orbitals for bonding.
- s orbital — a spherical region of electron probability.
- p orbital — a dumbbell-shaped orbital, oriented along x, y, or z axis.
- Degenerate orbitals — orbitals with the same energy.
- Sigma (σ) bond — bond formed by head-on orbital overlap.
- Pi (π) bond — bond formed by side-by-side overlap of unhybridized p orbitals.
Action Items / Next Steps
- Practice identifying hybridization and counting sigma and pi bonds in molecular structures.
- Review electron configurations and orbital diagrams for main group elements.