Closed-Shell and Chemical Bonding Effects are Almost Negligible in Two-Digit Z Elements

Abstract

In an atom, the total binding energy of Z electrons is close to E_GG = Z^2.4 rydberg, with observed (available up to Z = 17) and calculated non-relativistic values decreasing from 1.036 E_GG for Z = 5 to 0.996 E_GG for Z = 90; and relativistic values going through a shallow minimum 1.022 E_GG (Z = 26) back to 1.083 E_GG (Z = 90). Hence, closed-shell effects are about one percent of E_GG for neon (Z = 10), below 0.1 percent for krypton (Z = 36), and a few times 10^-5 for radon (Z = 86). Typical chemical bonding is 10 to 20 times weaker per atom than the closed-shell effects. The correlation energy (in atoms) is roughly −(0.7 eV)Z^1.2 (proportional to the square-root of E_GG). It is minute, but may well modify the radial extension (in compounds) and the LCAO model a lot. The virial theorem and spin-pairing energy are shortly reviewed. The feasibility of quantumchemistry for compounds involving two-digit Z values is critically reconsidered.