Chemical Bonding II: Valence and Molecular Orbital Theory

Valence Bond Theory

Covalent bonds are formed by overlap of atomic orbitals, each of which contains 1 electron of opposite spin.

Orbital Overlap

The greater the amount of orbital overlap, the stronger the bond.

Hybridization

The mixing of atomic orbitals to generate new sets of orbitals that then are available to form covalent bonds with other atoms.

sp Hybridization

Mixed 1 s atomic orbital with 1 p atomic orbital, resulting in 2 unhybridized p atomic orbitals.

sp2 Hybridization

Mixed 1 s atomic orbital with 2 p atomic orbitals, resulting in one unhybridized p atomic orbital.

sp3 Hybridization

Mixed 1 s atomic orbital with 3 p atomic orbitals, resulting in no unhybridized p atomic orbitals.

Steric Number

Indicates the number of hybrid orbitals for the atom.

σ Bond

Involves 'head-on' overlap.

π Bond

Involves 'side-on' overlap.

Single Bond

Consists of 1 σ bond.

Double Bond

Consists of 1 σ and 1 π bond.

Triple Bond

Consists of 1 σ and 2 π bonds.

Atomic Orbital

A wave function whose square gives the probability of finding an electron within a given region of space in an atom.

Molecular Orbital

A wave function whose square gives the probability of finding an electron within a given region of space in a molecule.

Bonding Orbital

Describes regions of increased electron density between nuclear centers that serve to hold atoms together in molecules.

Antibonding Orbital

Describes regions of electron density in a molecule that destabilize the molecule because they do not increase the electron density between nuclear centers.

Bond Order

The number of bonds between atoms: 1 for a single bond, 2 for a double bond, 3 for a triple bond.

Hybrid Atomic Orbital

One of a set of equivalent orbitals about an atom created when specific atomic orbitals are mixed.

Molecular Orbital Theory

Describes the formation of molecular orbitals by combining atomic orbitals on different atoms.

Bond Order Calculation

Bond order = (# bonding e− - # antibonding e−) / 2.

Resonance Hybrids

Combines the concepts of Valence Bond Theory and Molecular Orbital Theory to explain the delocalization of electrons.

MO Diagram

A basic representation of molecular orbitals, such as for H2, H2+, He2.

Electron Occupation of MO's

Electrons occupy MO's beginning with the MO of lowest energy, with a maximum of 2 electrons per orbital, and their spins are paired.