The Major Models
Valence Bond Theory (VBT) an early bonding theory that has developed into Modern valence bond theory. VBT views bonds as weakly coupled orbitals with each atom sharing a valence electron in a manner governed by the octet or 18 electron rule. Lewis structures are a representation of VBT's most basic bonding while molecular geometry is derived from orbital hybridization. Orbital hybridization is often taught with VESPR Theory despite significant differences in the underlying theory.
Valence shell electron pair repulsion (VSEPR) Theory The simplest and most primitive of the theories currently taught. Describes molecular geometry through the repulsion of electron fields which include bonds and lone pairs. It does not require any application of orbital shape.
Crystal Field Theory (CFT) This approximation begins with the geometries of the d orbitals derived from quantum mechanics. Ligands with their electron density are assumed to destabilize the metal d orbitals they interact with raising their energy while the remain d-orbitals drop in energy to balance the overall change in energy.
Ligand Field Theory (LFT) Considered a hybrid of CFT and MO Theory or simple an approximate application of MO Theory to transition metal complexes.
Molecular Orbital (MO) Theory A current and often applied model of molecular bonding. MO Theory assumes that bonds are derived from a linear combination of atomic orbitals. In this linear combination each pair of atomic orbitals involved in bonding results in a bonding and anti-bonding orbital. The destabilized of orbitals of CFT are now seen as anti-bonding component of orbitals that have overall been stabilized through bonding interactions.
Read more about this topic: Chemical Bonding Model
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