Barium atomization enthalpy

Barium is almost as powerful a reducing agent as is Cs. but La is somewhat less so. The appropriate sums of the ionization energies and the enthalpies of atomization compete well with the enthalpies of hydration for Cs and Ba, but the enthalpy of hydration of the La 1"1" ion is not sufficiently negative to outweigh the large third ionization energy. 

There is a 1-2% enhancement of the enthalpies of hydration of barium chloride by the substitution of D2O for H2O but it is impossible to determine whether this is a primary isotope effect resulting from changes in the strengths of the interactions of H atoms with neighbouring atoms or a secondary effect involving the interaction of the O atoms. ... 

Q Explain why the value of the enthalpy of atomization of barium seems not to show a major relativistic effect. 

Using the enthalpy of atomization of barium monochloride AatH° (Bad, 0) = 440.0 kJ/mol (IVTANTERMO, 2004), we calculated the enthalpies of atomization of RCl molecules from the enthalpies of reactions (1)-(14) collected in Table 74. The results are presented in Table 75 (columns 2-5). 

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