In my chemistry course, the addition of the "per" prefix generally means that the oxoanion of relevance will have one more oxygen than the "base" ion.
e.g. chlorate = ClOX3X−, perchlorate = ClOX4X−
However, permanganate is MnOX4X− and manganate is MnOX4X2−. The charges are different but there are still four oxygen atoms in each, so it seems to violate the convention. Any thoughts?
