LCAO: See Linear Combination of Atomic Orbitals.

LCFT: See Ligand and Crystal Field Theories.

LFSE: See Ligand Field Stabilization Energy.

LUMO: See Lowest Unoccupied Molecular Orbital.

Labile: A species is labile if it has a high kinetic reactivity.

Larmor frequency: The frequency at which a magnetic nucleus comes into resonance in a magnetic field of given strength.

Latimer Diagram: This is a means of presenting the reduction potentials for transitions between different oxidation states of the same element.

Lattice Energy: The energy for the reaction of the infinitely separated ions to give the solid. It measures the electrostatic interaction between the ions.

Lattice Parameter: The length of the crystal unit cell. There are three lattice parameters, one for the length along each of the axes.

Lattice: The periodic array of points which make up the crystal structure.

Le Chatelier’s principle: “A system at equilibrium, when subjected to a disturbance, responds in a way that tends to minimize the effect of the disturbance.”

Lewis Acid: A compound which can act as an electron pair acceptor.

Lewis Base: A compound which can act as an electron pair donor.

Lewis Representation: This is a scheme for drawing the structure of molecules, and shows the electrons in the molecule in terms of shared, bonding, pairs of electrons, and unshared, non-bonding or lone, pairs of electrons.

Ligand Field Spectra: These are the spectra generated by the ligand field transitions.

Ligand Field Splitting Parameter: This is the magnitude of the separation of the otherwise degenerate d-orbital levels when exposed to the ligand field. It is given the symbol Δo in an octahedral field and Δt in a tetrahedral field.

Ligand Field Stabilization Energy: The sum of the energies of the d-electrons in a transition metal ion complex compared to their energies in the uncomplexed metal ion.

Ligand Field Theory: The description of the effect on the metal ion energy levels when in a complex, based on the molecular orbital description of covalent bond formation between the ligands and the metal ion center.

Ligand Field Transitions: These are transitions of electrons between levels which are split in energy due to the effect of the ligand field.

Ligand and Crystal Field Theories: See Crystal Field Theory and Ligand Field Theory.

Ligand: An ion or molecule which bonds to a metal ion to form a complex, but which can exist in its own right in the absence of the complex.

Linear Combination of Atomic Orbitals (LCAO): An approximate procedure for forming molecular orbitals, by writing them as linear combinations of atomic orbital wavefunctions.

Linear Combination: A linear combination of two quantities means simply their sum or their difference.

Lone Pair: An electron pair in the valence shell of an atom which does not participate in bonding, i.e. it is associated with only one atom.

Lowest Unoccupied Molecular Orbital: The molecular orbital which has the lowest energy level of those levels which do not contain electrons.