How does chemical bonding lower the total energy of a group of atoms?

Chemical bonding occurs because atoms interact to reach a state of lower total energy than they would possess individually. When atoms approach one another, their nuclei and electrons redistribute in space to achieve this more stable, lower-energy arrangement.1

The mechanism for this energy reduction depends on the type of bonding:

• Covalent Bonding: According to molecular-orbital theory, atomic orbitals combine to form molecular orbitals. Electrons occupy a "bonding molecular orbital," which exists at a lower energy level than the original atomic orbitals. By sharing electron pairs, atoms can achieve a closed-shell configuration (often described by the octet rule), which minimizes energy by filling stable shells.23
• Ionic Bonding: This results from the electrostatic force of attraction between oppositely charged ions. When valence electrons are transferred to form a cation and an anion, the resulting electrostatic attraction creates a stable, low-energy crystalline structure.24

In both cases, the system is energetically favored to transition from a state of higher energy to one of lower energy.2