Ch 11

Theories of Covalent Bonding

Antibonding MO

A molecular orbital formed when wave functions are subtracted from each other, which decreases electron density between the nuclei and leaves a node. Electrons occupying such an orbital destabilize the molecule.

Bonding MO

A molecular orbital formed when wave functions are added to each other, which increases electron density between the nuclei. Electrons occupying such an orbital stabilize the molecule.

Homonuclear diatomic molecule

A molecule composed of two identical atoms

Hybrid orbital

An atomic orbital postulated to form during bonding by the mathematical mixing of specific combinattions of nonequivalent orbitals in a given atom.

hybridization

A postulated process of orbital mixing to form hybrid orbitals.

MO bond order

One-half the difference between the number of electrons in bonding MOs and the number in antibonding MOs.

Molecular orbital (MO)

An orbital of given energy and shape that extends over a molecule and can be occupied by no more than two paired electrons.

Molecular orbital diagram (MO) diagram

A depiction of the relative energy and the number of electrons in each MO, as well as the atomic orbitals from which the MOs form.

Molecular orbital (MO) theory

A model that describes a molecule as a collection of nuclei and electrons in which the electrons occupy orbitals that extend over the entire molecule

Nonbonding MO

A molecular orbital that is not involved in bonding.

pi bond

A covalent bond formed by sideways overlap of two atomic orbitals that has two regions of electron density, one above and one below the internuclear axis.

Pi MO

A molecular orbital is formed by a combination of two atomic (usually p) orbitals whose orientations are perpendicular to the internuclear axis

sigma bond

A type of covalent bond that arises through end-to-end orbital overlap and has most of its electron density along an imaginary line joining the nuclei

sigma MO

A molecular orbital that is cylindrically symmetrical about an imaginary line that runs through the nuclei of the component atoms

Sp hybrid orbital

An orbital formed by the mixing of one s and one p orbital of a central atoms

sp2 hybrid orbital

An orbital formed by the mixing of one s and two p orbitals of a central atom

sp3 hybrid orbital

An orbital formed by the mixing of one s and three p orbitals of a central atom

sp3d hybrid orbital

An orbital formed by the mixing of one s, three p, and one d orbital of a central atom

sp3d2 hybrid orbital

An orbital formed by the mixing of one s, three p, and two d orbitals of a central atom

Valence bond (VB) theory

A model that attempts to reconcile the shapes of molecules with those of atomic orbitals throught the concepts of orbital overlap and hybridization.