Hybridisation and Valence Bond Theory

Hybridisation

Mixing of atomic orbitals to form stable, directional hybrid orbitals that determine molecular shape

Valence electrons

Only these electrons are used in the hybridization process

Orbitals involved in hybridisation

s, p, d, f

sp hybridisation

Linear geometry, bond angle = 180°

sp2 hybridisation

Trigonal planar geometry, bond angle = 120°

sp3 hybridisation

Tetrahedral geometry, bond angle = 109.5° (109°28′)

sp3d (dz2)

Trigonal bipyramidal geometry

sp3d (dx2-y2)

Square-based pyramidal geometry

sp3d2 hybridisation

Octahedral geometry

sp2d hybridisation

Square planar geometry

Molecular Orbital Theory (MOT)

Atomic orbitals combine to form molecular orbitals that are centered on both nuclei

LCAO

Linear Combination of Atomic Orbitals, used to form molecular orbitals

Bonding molecular orbital

Formed by constructive overlap; increases electron density between nuclei

Antibonding molecular orbital

Formed by destructive overlap; has a node between nuclei; denoted with an asterisk (*)

Wave function symbol for bonding orbital

ΦB = ψx + ψy

Wave function symbol for antibonding orbital

ΦA = ψx - ψy

Sigma (σ) bond

Head-on overlap of atomic orbitals along the bond axis

Pi (π) bond

Lateral overlap of p orbitals; electron density is above and below the bond axis

Delta (δ) bond

Face-to-face overlap of two d orbitals

Order of molecular orbital energies

σ1s < σ1s < σ2s < σ2s < σ2p < π2p = π2p < π2p = π2p < σ*2p

Bond order formula

(Number of bonding electrons - Number of antibonding electrons) ÷ 2

Bond order = 1

Indicates a single bond

Bond order = 2

Indicates a double bond

Bond order = 3

Indicates a triple bond

Paramagnetic

Contains unpaired electrons in MO diagram

Diamagnetic

All electrons are paired in MO diagram