Periodicity in the isotope chemistry of hydrogen

Periodicities and regularities are established among the deuterium to protium isotopic reduced partition function ratios, ln(s/s')f, of 39 diatomic and 19 polyatomic hydrides. It is shown that ln(s/s')f for diatomic hydrides can be correlated with the position in the periodic table of the element X in the hydride HX. A similar analysis is made for the contributions from X-H stretching motion in the polyatomic hydrides H(n)X. It is shown that the contributions from stretching motions to ln(s/s')f in diatomic and polyatomic molecules are a linear function of the square root of the stretching force constants. The contributions from bending coordinates to ln(s/s')f depend on both the molecular structure of the hydride and the bending force constant. Simple correlations are established for the bending contributions to ln(s/s')f for the hydrides of the elements belonging to a common group in the periodic table. Four periodic rules of the isotope chemistry of hydrogen summarize and classify the data on the isotopic partition function ratios and the isotopic differences in free energies of formation of hydrides.