The Lighter Pairs

Most data on VPIE s for heavier pairs are at or below the normal boiling point, Tr-0.7. Of the critical property IE s, ln(Tc /Tc) is the easiest to measure and the most reliably known. Often lnlPc /Pd, and very often ln(pc /pc), are unknown or imprecisely known, and IrHp /p) has been measured only at or near room temperature or must be estimated. 

VPIE s of H20/D20 and LV fractionation factors for H20/H0D and H20/H2180 have been carefully measured and thoroughly interpreted over the complete coexistence range. Data for H20/T20 and intermediate isotopomer pairs are limited to lower temperatures. Liquid molar density IE data are complete for H20/D20. Departures from the law of geometric mean are small and the liquid molar density IE for H20/H0D is available to good precision. At low temperature, ln(p7p) for H20/D20 (and presumably for the other water isotopomer pairs) shows a minimum which has been ascribed to H-bonding ( water-structure effects ). 

A CS treatment of liquid phase molar densities, liquid MpIE s, and vapor pressures and VPIE s has been described. Quantization, necessary for the proper treatment of thermodynamic isotope effects, was introduced by using measured or correlated IE s on critical temperature, ATC = Tc — Tc, critical pressure, APC = Pc —Pc, and criti- 

Hirschfelder, J. O., Curtiss, C. F., Bird, R. B., Molecular Theory of Gases and Liquids, Wiley, New York, 1954. 

Polyakov, V. B., Horita, J., Cole, D. R. and Chialvo, A. A. Novel corresponding-states principle approach for the equation of state of isotopologues H2180 as an example. J. Phys. Chem. B-lll, 393 (2007). 

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Chemically, it is clear that Zn and Cd are rather similar and that Hg is somewhat distinct. The lighter pair are more electropositive, as indicated both by their electronegativity coefficients and electrode potentials (Table 29.1), while Hg has a... 

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