MCQ Detailed View

The Molecular Orbital (MO) Theory explains how electrons are distributed in molecules. According to this theory, atomic orbitals combine to form molecular orbitals, which extend over the entire molecule. These molecular orbitals can be bonding or antibonding.

Bonding molecular orbitals are formed by constructive interference of atomic orbitals, lowering the energy and stabilizing the molecule. Antibonding molecular orbitals result from destructive interference, raising the energy and destabilizing the molecule. The electrons in antibonding orbitals are represented with an asterisk () in notation, such as σ or π*.

Because MO theory emphasizes the role of antibonding orbitals in determining molecular stability, it is sometimes referred to as the Antibonding Theory. It provides a more accurate explanation of magnetic properties, bond order, and electronic configuration of molecules, which cannot be explained by simpler bonding theories like the Lewis structure or Valence Bond Theory.

MO theory applies to diatomic molecules like H₂, O₂, and N₂, predicting whether they are paramagnetic or diamagnetic based on the occupancy of antibonding orbitals. For example, O₂ has two unpaired electrons in π* orbitals, making it paramagnetic, a property correctly explained by MO theory.

The theory distinguishes between σ and π molecular orbitals and their corresponding antibonding orbitals. It also introduces the concept of bond order, calculated as half the difference between bonding and antibonding electrons. A positive bond order indicates a stable molecule, while a bond order of zero means the molecule cannot exist.

Understanding MO theory as Antibonding Theory is essential in physical chemistry for studying molecular stability, chemical reactivity, and spectroscopy. It bridges the gap between atomic theory and molecular structure, providing insight into how electron distribution affects molecular properties.