Molecular Orbital

A molecular orbital is formed by overlap/hybridization of atomic orbitals of different atoms. Likewise, we obtain atomic orbitals (1s, 2s, 2p) by solving the Schrödinger equation, we obtain the molecular orbitals ($1\sigma$, $1\sigma^*$, $2\sigma$, $2\sigma^*$, $1\pi_a$, $1\pi_b$) by solving the Schrödinger equation for H₂⁺ molecule (two protons and one electron). For a molecule, we can express the electronic configuration in terms of molecular orbitals following Pauli exclusion principle.

For example, Li₂ is expressed as: $(1\sigma)^2 (1\sigma^*)^2 (2\sigma)^2$.

Bonding order = [(number of bonding electrons) - (number of anti-bonding electrons)]/2

Li₂ has bonding order (4 - 2)/2 = 1. Higher the boding order, more stable the molecule is.