Energy diagram for hydrogen molecule.
Continuing our basic preview of important chemistry concepts in the context of basic mechanics, let us introduce the concept of bond dissociation energy.
This is a preview of concepts you will cover in much more depth in a few weeks in Chemical Bonding. Bond dissociation energy is the binding energy of two atoms in a covalent bond, a system with negative electron density (bonding electrons) between two positively charged nuclei.
Molecular orbital theory, a quantum theory, accounts for the array of possible states for the system. However, it is still very helpful to use the concepts of classical physics in work & energy and classical electrodynamics to help conceptualize the potential energy of the system. The electrons within the internuclear space, the bonding electrons, exert electric force, holding the nuclei of the bonded atoms within the chemical bond.
To understand the energy description of the covalent bond, it can be helpful to picture bond formation, the reverse of bond dissociation. Picture two unbonded atoms coming together to form a bond. As the two atoms near one another, electron density migrates into the internuclear distance (the space between the atoms), drawing the nuclei inwards. Picture the bonding electrons, a negative charge density, pulling the atoms together, as they fall into a potential energy well.