JNTU B.Tech I Year CHEMISTRY Previous Question Paper (September/October - 2021 - R18)

Molecular Orbital Theory (MOT) describes the electronic structure of molecules by considering electrons as moving under the influence of all nuclei in the molecule. Its key postulates are:

• Atomic orbitals of comparable energy and proper symmetry combine to form an equal number of molecular orbitals (MOs).
• When two atomic orbitals combine, they form one bonding molecular orbital (lower energy, higher stability) and one antibonding molecular orbital (higher energy, lower stability).
• Electrons are filled into molecular orbitals according to the Aufbau principle, Pauli exclusion principle, and Hund's rule, starting from the lowest energy level.
• Bonding orbitals result from constructive interference of atomic wave functions, while antibonding orbitals result from destructive interference.
• The electron probability density in a molecule is given by the square of the molecular orbital wave function.

The nitrogen molecule (N2) has a total of 14 electrons. The molecular orbital configuration is: σ1s², σ*1s², σ2s², σ*2s², π2px² = π2py², σ2pz².

The molecular orbital energy level diagram shows that the bonding orbitals (σ1s, σ2s, π2px, π2py, σ2pz) are filled with 10 electrons, and the antibonding orbitals (σ*1s, σ*2s) are filled with 4 electrons.

The bond order is calculated as:

Since all electrons in the molecular orbitals are paired, N2 is diamagnetic in nature.