CHM2005 Molecular Orbital Theory Flashcards

Vocabulary flashcards for CHM2005 Molecular orbital theory lecture notes.

Born-Oppenheimer approximation

Assumes that the motion of the nuclei can be completely ignored while solving the Schrödinger equation for the electron(s).

Molecular Orbitals

The natural successors of the atomic orbitals in the limit of two or more distinct nuclear centres. They share properties with atomic orbitals, including a maximum occupancy of 2 electrons, orbital angular momentum, and energy quantization at fixed R.

Potential Energy Curves

In diatomic molecules, represents the energy of the molecule at each value of R (internuclear separation).

Potential Energy Surfaces

For molecules with three or more atoms, represents the energy of the molecule considering multiple degrees of freedom. Determines nuclear motions (vibrations and rotations).

LCAO approximation

Linear Combination of Atomic Orbitals. A trial wavefunction that is a combination of the atomic wavefunctions on the individual atoms.

Bond Order

½ {(number of bonding electrons)-(number of antibonding electrons)}. The higher the bond order, the stronger the chemical bond.

Homonuclear

Meaning 'same nuclei,' refers to molecules where all atoms have the same nuclear charge (atomic number).

Parity

The behavior of the orbital wavefunction under the symmetry operation of inversion. Orbitals are labeled 'g' (gerade) if the sign remains the same and 'u' (ungerade) if it changes.

Orbital Mixing

The interaction and combination of molecular orbitals of the same symmetry, leading to stabilization of lower energy orbitals and destabilization of higher energy orbitals.

Heteronuclear

Meaning 'different nuclei,' refers to diatomic molecules composed of atoms with different nuclear charges.

Term Symbols

Used to describe the electronic states of molecules, incorporating total spin (S) and the magnitude of the total electronic orbital angular momentum (Λ).

Point Group

A classification of a molecule based on its symmetry elements. The point group determines the symmetry labels of the molecular orbitals.

Walsh Diagrams

Diagrams that document the change in energy of molecular orbitals as the bond angle is changed.

Franck-Condon Principle

The assumption that the nuclei are frozen during the absorption process. The vibrational wavefunction in the initial state is projected vertically onto the final state.

Wigner-Witmer rules

Rules used to predict the molecular electronic states formed from a pair of atomic electronic states.