Chemistry: Chemical Bonding: Molecular Orbitals Theory and Example of Mot (For CBSE, ICSE, IAS, NET, NRA 2022)

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Molecular Orbitals Theory

  • The bonds are formed as a result of overlapping of the atomic orbitals belonging to the constituent atoms.
  • Molecular orbital theory (MOT) was developed by Fund and R. S. Mulliken in 1932.
  • The molecular orbital theory visualizes the bonding to be delocalized in nature i.e.. , spread over the whole molecule.
  • According to MOT, in the process of bond formation following are seen:
    • The atomic orbitals of the constituent atoms combine to generate new types of orbitals which are called as molecular orbitals. They are delocalized.
    • The atomic orbitals of comparable energies and of suitable symmetry combine to give rise to an equal number of molecular orbitals.
    • The available electrons fill the orbitals in the order of increasing energy as in the Aufbau principle.
Molecular Orbitals Theory

Example of Mot

  • The two hydrogen atoms have one electron each in 1-s orbitals.
  • In the process of bond formation of two hydrogen atoms can combine in two possible ways.
    • the MO wave function is obtained by adding two atomic wave functions
    • In the other the MO is obtained by subtraction of the wave function.
  • The molecular orbital obtained by the addition of lower energy atomic orbitals is called a bonding orbital.
  • On the other hand, the orbital obtained by subtraction of higher energy atomic orbitals is called an anti-bonding orbital.
  • The molecular orbitals obtained are symmetric around the bond axis which is the line joining the two nuclei. Such molecular orbitals are called sigma molecular orbitals.
  • The bonding orbital obtained above is denoted as while the anti- bonding orbital is denoted as .
  • Here indicates the type of molecular orbital; 1-s is the atomic orbital involved and is the anti-bonding nature of the MO.
  • There are 2 electrons in a hydrogen molecule.
  • According to Aufbau principle, the orbital is a bonding orbital and it leads to stability or the bond formation.
  • The MO electronic configuration for molecule is written like electronic configuration of atoms.
  • The MO configuration of hydrogen molecule is given as .
  • The molecular orbital energy level diagram of H2 (a) and He2 (b) are given in the diagram below:
Example of Mot

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