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

Chemical bonding lowers the total energy of a group of atoms because the resulting bonded state is more stable than the state of the individual, separated atoms. This process is energetically favored, allowing the system to transition from a higher energy state to a lower one.1

In the context of covalent bonding, this energy reduction is explained by molecular-orbital theory. When atoms approach one another, their atomic orbitals combine to form molecular orbitals. Specifically, the electrons occupy a "bonding molecular orbital," which represents a region of space enveloping the nuclei. Because this bonding orbital exists at a lower energy level than the original atomic orbitals, the paired electrons occupy a state of reduced energy. The stability of the molecule stems from this occupation of the bonding combination, often characterized by an accumulation of electron density between the nuclei due to constructive interference.12

Similarly, in ionic bonding, the electrostatic attraction between oppositely charged ions creates a stable, low-energy arrangement where positive and negative charges balance one another.13