riamu
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why are transiition metal ions able to form ions with variable oxidation states
a typical answer at A-level will be because the differences in the succesive ionisation energies are similar to the differences in hydration enthalpies of the ions but what does hydration enthalpy has to do with ionisation energy?
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charco
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(Original post by riamu)
why are transiition metal ions able to form ions with variable oxidation states
a typical answer at A-level will be because the differences in the succesive ionisation energies are similar to the differences in hydration enthalpies of the ions but what does hydration enthalpy has to do with ionisation energy?
When the ions are in solution they are stabilised by the hydration enthalpy in the sense that a reaction spontaneity is determined by the Gibbs free energy change. This, in turn, is a function of the entropy and the enthalpy changes involved at a given temperature.

The hydration enthalpy is one of these enthalpy changes, and always contributes favorably as it is exothermic, whereas the ionisation enthalpy is endothermic. Hence, if both energy processes are roughly similar then they cancel out and the new oxidation state is as stable as the old one.

The is expressed simplistically, but is a valid argument.
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