A regularity exists between the heat of formation of alkali and alkaline earth oxysalts and the acidity and basicity of the oxides involved. The more basic an alkali or an alkaline earth oxide, the larger is the exothermic heat of formation of its oxysalts from the component oxides. Likewise, the more acidic the nonmetal oxide, the larger is the exothermic heat of formation of its salts from the component oxides. Although this is expectable in a general way, the regularity and consistency of these rules are rather surprising.The exothermic heat of formation from the oxides of different oxysalts of the same metal increases when the nonmetal changes through the sequences: B, C, N, and Si, P, S, Cl. This is explained in light of the increasing covalent character (or increasing polarization) of the oxygenhyphen;nonmetal bonds through the same series of elements.The exothermic heat of formation of polymerized oxysalts from the component oxides (borates, silicates, phosphates, pyrosulfates) is larger per equivalent than for the corresponding simple oxysalts. This is qualitatively explained as a result of the oxygenhyphen;nonmetal bond being less polarized or more ionic in a polymerized salt than in the nonpolymerized salt with the same central atom in the oxyanion.The heat of salt formation per equivalent increases numerically when the metal changes from Li to Cs, or from Mg to Ra. This is related to the increase of the crystal energy of the corresponding metal oxides.
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