# Why does iodine get oxidized to iodic acid and not periodic acid by nitric acid?

Nitric acid oxidizes iodine to iodic acid, $\ce{HIO3}$ and not periodic acid, $\ce{HIO4}$, which is of a higher oxidation state. This happens although other nonmetals are oxidized to their highest oxidation state. How can this be explained?

Nitric acid is not strongly oxidizing enough to get iodine to +7. Relativistic effects tend to make the $s$ subshell valence electrons more stable than the others in heavy atoms (http://www.annualreviews.org/doi/abs/10.1146/annurev-physchem-032511-143755), so to some extent iodine acts as if it has only five valence electrons. To pull out those last two electrons and get periodic acid, electrochemical oxidation is commonly used with a very high oxidation potential (https://en.wikipedia.org/wiki/Periodic_acid).