Molecular Orbital Theory Molecular Orbital Theory In chemistry, molecular orbital (MO) theory is a method for determining molecular structure in which electrons are not assigned to individual bonds between atoms, but are treated as moving under the influence of the nuclei in the whole molecule. In this theory, each molecule has a set of molecular orbitals, in which it is assumed that the molecular orbital wave function ψj may be written as a simple weighted sum of the n constituent atomic orbitals χi, according to the following equation: The cij coefficients may be determined numerically by substitution of this equation into the Schrödinger equation and application of the variational principle. This method is called the linear combination of atomic orbitals (LCAO) approximation and is used in computational chemistry. An additional unitary transformation can be applied on the system to accelerate the convergence in some computational schemes. Molecular orbital theory was seen as a competitor to valence bond theory in the 1930s, before it was realized that the two methods are closely related and that when extended they become equivalent.
Know More About :- Organic Chemistry Practice Problems Math.Tutorvista.com
Page No. :- 1/4
Linear Combination of Atomic Orbitals Molecular orbital theory is used to describe the atoms in terms of electronic configuration of electrons and the orbital arrangements. The orbitals give a clear picture of the geometry of the molecules. The molecular orbitals are obtained by the linear combination of atomic orbitals. 1. The molecular orbitals are filled in such a way that the energy of the molecule is minimum. 2. Orbitals which have the same energy are half filled with parallel spin before they begin to pair. 3. In an orbital, there can be a maximum of two electrons. The linear combination of atomic orbitals is employed to form the molecular orbitals. <<--- There are two types of molecular orbitals 1. Bonding molecular orbitals 2. Antibonding molecular orbitals In case of bonding molecular orbitals, the electrons spend most of their time in the region between the two nuclei. On the contrary, in case of antibonding molecular orbitals, the electrons spend most of the time away from the nuclei. Anti-bonding Molecular Orbital Theory The molecular orbital theory is a way for looking at the structure of a molecule by using molecular orbitals that belong to the molecule rather than to the individual atoms. When the bonding occurs between two atoms, the pair of electrons forms the bond occupying an MO. MO is a mathematical combination of the wave functions of the atomic orbitals of the two atoms involved. When atoms combine to form the molecule, the number of orbitals in the molecule is equal to the number of orbitals in the combining atoms.
Learn More :- Mastering Chemistry Answers Math.Tutorvista.com
Page No. :- 2/4
When two very simple atoms, with one atomic orbital, are combined, two molecular orbitals are formed. One is a bonding orbital, lower energy than the atomic orbitals, and derived from their sum. It is called sigma. The other is an anti-bonding orbital, higher energy than the atomic orbitals, and resulting from their difference. It is called sigma anti-bonding (Ď&#x192; *). The basic idea is illustrated by considering diatomic molecules of hydrogen and helium. Each hydrogen atom has one 1 s electron. In the H 2 molecule, the two hydrogen electrons will go into the lowest energy MO available. In the case of helium, every helium atom has two electrons. So, the He2 molecule would have four. Two will go into the lower energy bonding orbital, and the other two would have to go into the higher energy sigma anti-bonding orbital.
Math.Tutorvista.com
Page No. :- 4/4
Thank You For Watching
Presentation