Provided that there are i electrons (i = n, n-1, n-2, …1) in an atom and assuming the interaction of proton-electron is shared by every electron, according to Coulomb's law, the other electrons will offset the proton-electron attraction. Ek is the molar kinetic energy of a surface electron, and n is the number of protons in a nucleus. The effect of interactions between two electrons on the surface may be negligible because the mass of a nucleus is much larger than that of an electron. Based on Eq. 48, for an H-1 atom (r0=53 pm), T=1.05×10 5 K, and then Ek=1.307×10 3 kJ/mol or 13.543 eV. The ionization energy recommended by NIST is 1.312×10 3 kJ/mol or 13.599 eV. This result indicates that the ionization energy is the kinetic energy of an electron.