MO Theory ( Molecular Orbital Theory )
- MO Theory was originally called Hund-Mulliken theory.
- The word orbital was introduced by mulliken in 1932.
- In a molecule electrons are present in new orbitals called MO.
- MO are formed by linear combination of atomic orbitals ( LCAO ) of equal energies ( homonuclear ) or comparable energies ( hetero nuclear molecule ). ( Details : The molecule H2 is composed of two hydrogen atoms. Both H atom have 1s orbital, so when bonded together there are two MO.
- Two atomic orbitals can combine to form two molecular orbital.One has a lower energy ( bonding MO ) and other has higher energy ( anti bonding ). ( Explain : Bonding MO helps to stablize a system of atoms since less energy. Anti bonding MO cause a system to be unstabilized. since more energy.
- Bonding MO are represented by σ (sigma ), π ( pi ) , δ ( delta ).
- Anti bonding MO are represented by σ * , δ*, π* .
- The MO are filled in the increasing order of their energies starting with orbitals of least energy. (Aufbau Principle ).
- MO can accommodate only two electrons and these two electrons must have opposite spin. ( Paul's Exclusion Principle )
- Every orbital in a sub level is singly occupied before any orbital is doubly occupied. All electrons in singly occupied orbitals have the same spin. ( Hund's Rule ).
Post a Comment