  Oxidation states are well-established in chemical science teaching and
research. We data-mine more than 168,000 crystallographic reports to find an
optimal allocation of oxidation states to each element. In doing so we uncover
discrepancies between text-book chemistry and reported charge states observed
in materials. We go on to show how the oxidation states we recommend can
significantly facilitate materials discovery and heuristic design of novel
inorganic compounds.
