Saturday, October 9, 2010
Molecular Orbital Model
Problems arise from the calculation of the electron distribution of settlement allowed for the Schrodinger equation of quantum mechanics, in which each settlement is known as a molecular orbital (MO) and related particular energy states and the distribution of electron pairs. In the orbital method molecule, the bond is considered formed from the atomic orbitals overlap. When there number of atomic orbitals overlap, the orbitals is lost and replaced by the orbital The same new. New orbitals formed called the orbital molecule. Different molecular orbitals with atomic orbitals. Includes both molecular orbital or more nuclei, whereas the atomic orbitals covers only one nucleus. In the localized bonding, the number of atomic orbitals that overlap are the two (each filled one electron) to produce two molecular orbitals. One of the orbitals it has a lower energy than the original atomic orbital energy, and called the bonding orbital. Another molecular orbital has higher energy than orbital origin called anti-bonding orbital.
In filling orbitals with electrons, low-energy orbitals fill first. Therefore, new bonding molecular orbital formed is able to accommodate two electron then the two electrons of each atomic orbital origin can now occupy the bonding orbital. In the ground state, the anti-bonding orbital contains no electrons. The more overlap that occurred more ties, although the total overlap limited by the core repulsion with each other.
Anti-bonding orbital has one node in the core-core, practically no electrons in the orbital area so that it can not be expected to binding very good. Molecular orbitals formed by overlap of two orbitals when sesumbu electron density center with the second core is called the orbital σ (sigma) and called σ bonds. Anti-bonding orbital of the accompanying marked with σ* Orbital σ not only formed from the overlap of two orbitals s but may also through orbital overlap another type of atom (s, p, d, or f), whether between the same orbitals ordifferent orbitals, the important thing is happening from the orbital overlap marked the same.
Fig. Two 1s orbitals overlap to produce σ and σ * orbitals
Orbital is often characterized by the properties of symmetry. σ* orbitals of hydrogen often ψg written. Letter g mark gerade. Gerade orbitals are the orbitals that do not sign will change when reflected through the center of symmetry. σ* orbitals are ungerade (Given the symbol ψu). Ungerade orbitals change sign when reflected through the center symmetry.
In molecular orbital calculations, a wave function defined as a linear combination of atomic orbitals have overlap. This method often called a linear combination of atomic orbitals (LCAO).Function is a function ψB ψA and the atomic orbitals A and B, CA and CB states weighting factor.
In the valence bond method, a wave function is written to each from a variety of electronic structure that allows owned by a molecules (each structure is called a canonical form), and the total obtained ψ through the summation of a number of canonical structure which seems reasonable, each with weight factor.
For example the canonical form of molecular hydrogen: