However, as two H atoms approach each other, the equilibrium distance is determined by two nuclei because of their vast masses relative to electrons. Since the Coulomb's force of proton-proton equals that of proton-electron, the equilibrium distance equals the radius of the H atom. Moreover, in contrast to the two electrons mentioned above, the velocities of the two electrons are the same. Hence, the equilibrium distance between two electrons is 2r0. However, the isothermal condition must be satisfied for bonding or pairing two electrons. Namely, the distance between two nuclei must equal that between the paired electrons and nuclei. Therefore, a sphere with the radius √ 𝑟 forms while two nuclei are rotating.