Valence Bond Theory
Valence Bonding Theory
Incorporates atomic orbitals of atoms, use of quantum theory
Dealing ONLY with orbitals involved in a covalent bond
Electron clouds of individual atoms OVERLAP when atoms form chemical bond
Valence Bonding Theory (cont.)
Covalent bond formation involves 2 electrons of opposite spins paired in an overlap of atomic orbitals with high electron density (p. 403)
Strong chemical bonds with more atomic overlap
Optimal orbital overlap---gives maximum bond strength
Key Points to Valence Bond Theory
1) Electrons generally like to stay in their normal orbitals (as if in isolated atom).
2) Electrons involved in a chemical bond hang out in an atomic orbital overlap.
3) The orientation of the atomic orbitals of the central atom determine its molecular geometry
4) Atomic orbitals with more than one axis (p orbital)– maximum overlap found when imaginary line connecting the atoms passes through the maximum overlap.
Hybridization
Electron configuration of Carbon (show only valence electrons)
**Atoms in a chemical bond do NOT have the same orbitals as in isolation **
Hybridization—General
Combines/Mixes atomic orbitals
Not an actual process, a method of visualizing and explaining molecular structure
Hybrid orbitals—
Mix of 2 types of orbitals
Back to Carbon
Combine/mix together “s ” and “p” orbitals
Result is 4 orbitals with same shape and energy
Hybridization—General (cont.)
Applies mostly to central atoms
# hybrid orbitals = # of combined orbitals
Hybrid orbitals can interact/overlap with regular or hybrid orbitals
Hybrid orbitals have different shapes and orientations from regular orbitals
Hybrid Orbitals
1) sp3 hybrid orbitals
Mixture of 1 s orbital and 3 p orbitals
Results in 4 hybrid orbitals
Tetrahedral structure, 109.5° bond angle
Ex. CH4—C
NH3---N
Hybrid Orbitals
2) sp2 hybrid orbitals
Seen a lot with double bonds
Mixture of 1 s orbital and 2 p orbitals
results in 3 hybrid orbitals
Trigonal planar structure, 120° bond angle
Ex. BF3
Hybrid Orbitals
3) sp hybrid orbitals
Seen a lot with triple bonds
Mixture of 1 s orbital and 1 p orbital
Results in 2 hybrid orbitals, 2 empty p orbitals
Linear structure, 180° bond angle
Ex. BeCl2
How do we discuss hybridization????
Focus on central atom
Each atomic orbital results in a hybrid orbital in chemical bond
ALL hybrid orbitals have electrons (lone or bonded pair)
Hybrid orbital orientation = electron group geometry
1) Determine electron group geometry
2) Find appropriate hybridization
3) Describe how the orbitals overlap to give molecular geometry
Electron Group
Electron Group Geometry
Hybridization
2 Linear sp
3 Trigonal planar
sp2
4 Tetrahedral
sp3
Ex. 1 Determine the hybridization of the central atom in…..
H3O+
Ex. 2 Determine the hybridization of the central atom in…..
NH3
Ex. 3 Determine the hybridization of the central atom in…..
CO2
Ex. 4 Determine the hybridization of the central atom in…..
O2
Homework Molecular Geometry (p. 427 #21, 23, 25,
27)
Hybridization (Read pp. 402-408, p. 428 #45-46)